Method and apparatus for harvesting biomechanical energy

ABSTRACT

Methods and apparatus are disclosed for harvesting energy from motion of one or more joints. Energy harvesters comprise: a generator for converting mechanical energy into corresponding electrical energy; one or more sensors for sensing one or more corresponding characteristics associated with motion of the one or more joints; and control circuitry connected to receive the one or more sensed characteristics and configured to assess, based at least in part on the one or more sensed characteristics, whether motion of the one or more joints is associated with mutualistic conditions or non-mutualistic conditions. If conditions are determined to be mutualistic, energy harvesting is engaged. If conditions are determined to be non-mutualistic, energy harvesting is disengaged.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/990,165, filed Feb. 8, 2008, which application is the national stageapplication of PCT/CA2006/001302, filed Aug. 10, 2006, which claims thebenefit of U.S. Provisional App. No. 60/707,232, filed Aug. 10, 2005.

TECHNICAL FIELD

This invention relates to methods and apparatus for convertingmechanical energy generated by humans and/or animals into electricalenergy. Harvested electrical energy can be used for a variety ofpurposes.

BACKGROUND OF THE INVENTION

Humans and other animals are a rich source of mechanical power. Ingeneral, this mechanical power is derived from chemical energy. Thechemical energy required for a muscle or group of muscles to perform agiven activity may be referred to as the “metabolic cost” of theactivity. In humans and other animals, chemical energy is derived fromfood. Food is generally a plentiful resource and has a relatively highenergy content. Humans and other animals exhibit a relatively highefficiency when converting food into chemical energy which then becomesavailable to muscles for subsequent conversion into mechanical energy.Mechanical power generated by humans and other animals can be efficient,portable and environmentally friendly.

As a consequence of the attractive characteristics of human power, therehave been a wide variety of efforts to convert human mechanical powerinto electrical power, including:

U.S. Pat. No. 1,472,335 (Luzy);

U.S. Pat. No. 1,184,056 (Van Deventer);

U.S. Pat. No. 5,917,310 (Baylis);

U.S. Pat. No. 5,982,577 (Brown);

U.S. Pat. No. 6,133,642 (Hutchinson);

U.S. Pat. No. 6,291,900 (Tiemann et al.).

A subset of the devices used to convert human mechanical power intoelectrical power focuses on energy harvesting—the capture of energy fromthe human body during everyday activities. Examples of disclosuresrelating to energy harvesting include:

-   Starner, T., Human-powered wearable computing. IBM Systems    Journal, 1996. 35(3-4): 618-629;-   Chapuis, A. and E. Jaquet, The History of the Self-Winding Watch.    1956, Geneva: Roto-Sadag S.A.;-   Shenck, N. S. and J. A. Paradiso, Energy scavenging with    shoe-mounted piezoelectrics. IEEE Micro, 2001. 21(3): 30-42;-   Kymissis, J., et al. Parasitic Power Harvesting in Shoes. in Second    IEEE International Conference on Wearable Computing. 1998: IEEE    Computer Society Press;-   Antaki, J. F., et al., A gait-powered autologous battery charging    system for artificial organs. Asaio J, 1995. 41(3): M588-95;-   Gonzalez, J. L., A. Rubio, and F. Moll. A prospect on the use of    piezolelectric effect to supply power to wearable electronic    devices. in ICMR. 2001. Akita, Japan;-   Moll, F. and A. Rubio. An approach to the analysis of wearable    body-powered systems. in MIXDES. 2000. Gdynia, Poland;-   Drake, J., The greatest shoe on earth, in Wired. 2001. p. 90-100;-   Niu, P., et al. Evaluation of Motions and Actuation Methods for    Biomechanical Energy Harvesting. in 35th Annual IEEE Power    Electronics Specialists Conference. 2004. Aachen, Germany: IEEE.-   U.S. Pat. No. 6,768,246 (Pelrine et al.);-   US patent publication No. US2004/0183306 (Rome);-   U.S. Pat. No. 6,293,771 (Haney et al.).

For a variety of reasons, the energy harvesting apparatus disclosed bythese authors have experienced limited power generation capacity and/orlimited commercial viability or success. Drawbacks of the prior artenergy harvesting apparatus contemplated in these disclosures include:lack of implementation detail; low power yield; and heavy and/or awkwardenergy harvesting apparatus, which can lead to relatively high metabolicenergy costs and correspondingly low energy conversion efficiency and/orimpairment of normal physical activity, for example.

There is a desire to provide improved methods and apparatus forharvesting biomechanical energy.

BRIEF SUMMARY OF THE INVENTION

One aspect of the invention provides an apparatus for harvesting energyfrom motion of one or more joints. In this aspect, the apparatuscomprises: a generator for converting mechanical energy intocorresponding electrical energy; one or more sensors for sensing one ormore corresponding characteristics associated with motion of the one ormore joints; and control circuitry connected to receive the one or moresensed characteristics and configured to assess, based at least in parton the one or more sensed characteristics, whether motion of the one ormore joints is associated with mutualistic conditions or non-mutualisticconditions. If the control circuitry determines that the motion of theone or more joints is associated with particular mutualistic conditions,the control circuitry is configured to engage energy harvesting bycompleting a coupling of mechanical energy associated with the motion ofthe one or more joints to the generator and electrical output of thegenerator to a load. If the control circuitry determines that the motionof the one or more joints is associated with non-mutualistic conditions,the control circuitry is configured to disengage energy harvesting bydecoupling the mechanical energy associated with the motion of the oneor more joints from the generator and/or the electrical output of thegenerator from the load.

Another aspect of the invention provides an apparatus for harvestingenergy from motion of one or more joints. In this aspect, the apparatuscomprises: a generator for converting mechanical energy intocorresponding electrical energy; a mechanical coupling for transferringmechanical energy associated with motion of the one or more joints tothe generator; an electrical coupling for transferring electrical energyoutput of the generator to a load; one or more sensors for sensing oneor more corresponding characteristics associated with the motion of theone or more joints; and control circuitry connected to receive the oneor more sensed characteristics and configured to assess, based at leastin part on the one or more sensed characteristics, whether motion of theone or more joints is associated with mutualistic conditions ornon-mutualistic conditions. If the control circuitry determines that themotion of the one or more joints is associated with non-mutualisticconditions, the control circuitry is configured to disengage themechanical energy transfer of the mechanical coupling and/or theelectrical energy transfer of the electrical coupling.

Another aspect of the invention provides an apparatus for harvestingenergy from motion of a joint. In this aspect, the apparatus comprises:a generator for converting mechanical energy into correspondingelectrical energy; a mechanical coupling for transferring mechanicalenergy associated with motion of the joint to the generator; and anelectrical coupling for transferring electrical energy output of thegenerator to a load. The joint may be the knee joint.

Another aspect of the invention provides a method for harvesting energyfrom motion of one or more joints. In this aspect, the method comprises:providing a generator for converting mechanical energy intocorresponding electrical energy; sensing one or more characteristicsassociated with motion of the one or more joints; and assessing, basedat least in part of the one or more sensed characteristics, whethermotion of the one or more joints is associated with mutualisticconditions or non-mutualistic conditions. If the motion of the one ormore joints is determined to be associated with particular mutualisticconditions, energy harvesting is engaged by completing a coupling ofmechanical energy associated with the motion of the one or more jointsto the generator and electrical output of the generator to a load. Ifthe motion of the one or more joints is determined to be associated withnon-mutualistic conditions, then energy harvesting is disengaged bydecoupling the mechanical energy associated with the motion of the oneor more joints from the generator and/or the electrical output of thegenerator from the load.

Another aspect of the invention provides a method for harvesting energyfrom motion of a joint. In this aspect, the method comprises: providinga generator for converting mechanical energy into correspondingelectrical energy; mechanically coupling the joint to the generator totransfer mechanical energy from the joint to the generator; andelectrically coupling the electrical energy output from the generator toa load. The joint may comprise the knee joint.

Another aspect of the invention provides an apparatus for harvestingenergy from motion of one or more joints. In this aspect, the apparatuscomprises: means for converting mechanical energy associated with themotion of the one or more joints into electrical energy; means forassessing whether the motion of the one or more joints is associatedwith mutualistic conditions or non-mutualistic conditions; means forcompleting a coupling of mechanical energy associated with the motion ofthe one or more joints to the converting means and electrical output ofthe converting means to a load if the assessing means determines thatthe motion of the one or more joints is associated with particularmutualistic conditions; and means for disengaging the mechanical energyassociated with the motion of the one or more joints from the convertingmeans and/or electrical output of the converter from the load, if theassessing means determines that the motion of the one or more joints isassociated with non-mutualistic conditions.

Another aspect of the invention provides an apparatus for harvestingenergy from motion of one or more joints. In this aspect, the apparatuscomprises: a generator coupled to the one or more joints and to a loadfor converting mechanical energy associated with motion of the one ormore joints into corresponding electrical energy delivered to the load;one or more sensors for sensing one or more correspondingcharacteristics associated with motion of the one or more joints; andcontrol circuitry connected to receive the one or more sensedcharacteristics and configured to assess, based at least in part on theone or more sensed characteristics, whether motion of the one or morejoints is associated with mutualistic conditions or non-mutualisticconditions. If the control circuitry determines that the motion of theone or more joints is associated with non-mutualistic conditions, thecontrol circuitry is configured to decouple the generator from the oneor more joints and/or the generator from the load.

Another aspect of the invention provides a method for harvesting energyfrom motion of one or more joints. In this aspect, the method comprises:providing a generator coupled to the one or more joints and to a loadfor converting mechanical energy associated with motion of the one ormore joints into corresponding electrical energy delivered to the load;sensing one or more characteristics associated with motion of the one ormore joints; and assessing, based at least in part of the one or moresensed characteristics, whether motion of the one or more joints isassociated with mutualistic conditions or non-mutualistic conditions. Ifthe motion of the one or more joints is determined to be associated withnon-mutualistic conditions, then the method comprises decoupling thegenerator from the one or more joints and/or the generator from theload.

Further aspects of the invention, further features of specificembodiments of the invention and applications of the invention aredescribed below.

The foregoing and other objectives, features, and advantages of theinvention will be more readily understood upon consideration of thefollowing detailed description of the invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A schematically depicts a positive mechanical operational mode ofa muscle wherein the muscle is used to generate movement of one or moreassociated body segment(s).

FIG. 1B schematically depicts a negative mechanical operational mode ofa muscle wherein the muscle is used to decelerate movement of one ormore associated body segment(s).

FIG. 2 shows a number of plots representative of various quantitiesrelating to the typical dynamics of a knee joint during one full cycleof a walking movement.

FIG. 3A schematically depicts non-mutualistic energy harvesting during apositive mechanical power mode of an associated muscle.

FIG. 3B schematically depicts mutualistic energy harvesting during anegative mechanical power mode of an associated muscle.

FIG. 4A shows an energy harvesting apparatus according to a particularembodiment of the invention wherein the energy harvester is mountable onthe body of a host.

FIG. 4B shows an energy harvesting apparatus according to anotherembodiment of the invention wherein the energy harvester is embedded ina prosthetic limb.

FIG. 4C shows an energy harvesting apparatus according to anotherembodiment of the invention wherein the energy harvester is implantedunder the skin of the host.

FIG. 5A is a schematic block diagram of an energy harvesting apparatusaccording to a particular embodiment of the invention.

FIG. 5B is a schematic block diagram showing a method for determiningwhen to engage the FIG. 5A energy harvesting apparatus to harvest energyunder mutualistic conditions according to a particular embodiment of theinvention.

FIGS. 6A and 6B are respectively side and front views of an energyharvesting apparatus according to another embodiment of the invention.

FIG. 7 is a partial exploded view of the FIG. 6A-6B energy harvestingapparatus.

FIG. 8 is a schematic block diagram of the FIG. 6A-6B energy harvestingapparatus.

FIG. 9 is a schematic block diagram showing a method for determiningwhen to engage the FIG. 6A-6B energy harvesting apparatus to harvestenergy under mutualistic conditions according to a particular embodimentof the invention.

FIG. 10 shows a number of plots relating to the harvesting of energywhile the host is walking using the FIG. 6A-6B energy harvestingapparatus in accordance with the method of FIG. 9.

FIG. 11 is a schematic block diagram showing a method for determiningwhen to engage the FIG. 6A-6B energy harvesting apparatus to harvestenergy under mutualistic conditions according to another embodiment ofthe invention.

FIG. 12 is a schematic block diagram of an energy harvesting apparatusaccording to another embodiment of the invention.

FIGS. 13A and 13B are respectively isometric and exploded isometricviews of a bi-directional energy harvesting apparatus according to aparticular embodiment of the invention.

FIG. 14 is a schematic block diagram of the FIG. 13A-13B energyharvesting apparatus.

FIG. 15 is a schematic block diagram showing a method for determiningwhen to selectively harvest energy using the FIG. 13A-13B energyharvesting apparatus according to a particular embodiment of theinvention.

FIG. 16 shows a number of plots relating to the harvesting of energywhile the host is walking using the FIG. 13A-13B energy harvestingapparatus in accordance with the method of FIG. 15.

FIG. 17 is a schematic block diagram showing a method for determiningwhen to selectively harvest energy using the FIG. 13A-13B energyharvesting apparatus according to another embodiment of the invention.

FIG. 18 shows a number of plots relating to the harvesting of energywhile the host is walking using the FIG. 6A-6B energy harvestingapparatus configured to harvest energy under mutualistic andnon-mutualistic conditions.

FIG. 19 is a schematic block diagram showing a method for determiningwhen to selectively harvest energy using the FIG. 4B energy harvestingapparatus according to a particular embodiment of the invention.

FIG. 20 is a schematic block diagram showing a method for determiningwhen to selectively harvest energy using the FIG. 4C energy harvestingapparatus according to a particular embodiment of the invention.

FIGS. 21A, 21B and 21C respectively depict EMG plots showing muscleactivity levels and electrical power generation for a human walking withno energy harvesting, with mutualistic energy harvesting (associatedwith knee extension only) and with both mutualistic and non-mutualisticenergy harvesting (associated with knee extension only).

FIG. 22 shows a plot of heart rate versus time for a human walking withno energy harvesting, with mutualistic energy harvesting (associatedwith knee extension only) and with both mutualistic and non-mutualisticenergy harvesting (associated with knee extension only).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Throughout the following description, specific details are set forth inorder to provide a more thorough understanding of the invention.However, the invention may be practiced without these particulars. Inother instances, well known elements have not been shown or described indetail to avoid unnecessarily obscuring the disclosure. Accordingly, thespecification and drawings are to be regarded in an illustrative, ratherthan a restrictive, sense.

FIG. 1A schematically depicts a positive mechanical power operationalmode 10 of a muscle 12, wherein muscle 12 is used to generate mechanicalenergy which results in corresponding movement of one or more associatedbody segment(s) 44 (e.g. limb(s)). In positive mechanical power mode 10,muscle 12 converts chemical energy into mechanical energy of associatedbody segment 44. Due to the inefficiency of this conversion process,muscle 12 also outputs heat energy when operating in positive mechanicalpower mode 10. Positive mechanical power mode 10 is associated with theshortening of muscle 12. Shortening of muscle 12 can pull associatedbody segment 44 around a joint (not shown), for example. For someactivities, the efficiency of positive power production can approach25%. With such an efficiency, for muscle 12 to generate 1 W ofmechanical power requires a metabolic cost of 4 W and the remaining 3 Wis dissipated as heat.

FIG. 1B schematically depicts a negative mechanical power operationalmode 20 of muscle 12, wherein muscle 12 acts to brake (i.e. decelerate)the motion of the associated body segment(s) 44, thereby reducing themechanical energy of body segment 44 and causing body segment 44 todecelerate. Muscle 12 requires chemical energy to cause this brakingeffect. In negative mechanical power mode, muscle 12 uses chemicalenergy to reduce the mechanical energy of the associated body segmentand, in doing so, produces heat energy. Negative mechanical power mode20 is associated activity in a particular muscle 12 when that muscle 12is lengthening. During negative mechanical power mode, muscle 12 isactively generating force which tends to decelerate a lengthening ofmuscle 12. When muscle 12 operates in a negative mechanical power mode,associated body segment 44 may be moving around a joint in a directionthat causes muscle 12 to lengthen, but the activity of muscle 12 causesdeceleration of the rate of movement of associated body segment 44. Forsome activities, the efficiency associated with negative powerproduction can be as high as −120%. With such an efficiency, for muscle12 to produce −1 W of mechanical power requires a metabolic cost of 0.83W and 1.83 W is dissipated as heat.

During many activities, especially rhythmic activities like walking orrunning, muscles switch frequently between positive and negativemechanical power generation modes. Because muscles act on the body'sskeletal system, positive and negative muscle power may be seen (from anexternal perspective), as positive and negative joint power. FIG. 2presents a number of plots representative of various quantities relatingto typical dynamics of a knee joint during one full cycle 21 of awalking movement for a 58 kg subject walking at 1.3 m/s with a stepfrequency of 1.8 Hz:

-   -   Plot 22 represents the angle of the knee joint, where 0°        represents full extension and negative angles represent knee        flexion;    -   plot 24 represents the angular velocity of the knee joint (i.e.        the time derivative of plot 22), where positive angular velocity        represents movement in the knee extension direction and negative        angular velocity represents movement in the knee flexion        direction;    -   plot 26 represents the moment of the knee joint, where a        positive moment represents torque in the extension direction and        a negative moment represents torque in the flexion direction;    -   plot 28 represents the mechanical power associated with the knee        joint. Mechanical power (plot 28) represents the product of the        torque (plot 26) and the angular velocity (plot 24) of the knee        joint. The integral of the mechanical power (plot 28) represents        the mechanical work performed by the knee joint;    -   plot 30 represents rectified and filtered electromyographic        (EMG) signals representative of electrical activity generated by        the vastus lateralis (i.e. one of the quadricep muscles) which        is an example of a knee extensor muscle; and    -   plot 32 represents rectified and filtered EMG signals        representative of electrical activity generated by the        semitendinosus (i.e. one of the hamstrings) which is an example        of a knee flexor muscle.

Referring to FIG. 2, cycle 21 may generally be divided into a stancephase 21A, where the foot corresponding to the illustrated knee is onthe ground, and a swing phase 21B, where the foot corresponding to theillustrated knee is off of the ground. In the illustrated plots, heelstrike occurs at time t=0, where plot 22 shows that the knee is almostat full extension. At time t=0, the leg corresponding to the illustratedknee extends forwardly from the hip and represents the front one of thetwo legs. Immediately after time t=0, the knee begins to flex in region22A as weight is transferred to the corresponding leg. In region 22B,the illustrated knee rebounds and extends slightly during the swingphase of the other leg. In region 22C, the illustrated knee begins toflex again as it prepares for swing phase 21B. In region 22D, cycle 21enters swing phase 21B and the foot corresponding to the illustratedknee leaves the ground. The illustrated knee continues to flex in region22D. In region 22E, the knee begins to extend again as the correspondingleg swings forwardly again and prepares for another heel strike. Inregion 22F, the illustrated knee is relatively straight. The knee mayextend slightly beyond straight in region 22F immediately before heelstrike which marks the beginning of the next cycle.

Regions 28A and 28B of power plot 28 represent regions where at leastsome of the muscles associated with the illustrated knee are in negativemechanical power modes 20 (see FIG. 1B). In region 28A, the illustratedknee is flexing and the knee extensor muscles are lengthening, but atleast the illustrated knee extensor muscles are acting in a negativemechanical power mode 20 to counteract this flexion movement. Region 30Aof plot 30 shows how the illustrated knee extensor muscles are activeduring the time associated with region 28A. In region 28B, theillustrated knee is extending and the knee flexor muscles are extending,but at least the illustrated knee flexor muscles are acting in anegative mechanical power mode 20 to counteract this extension movement.Region 32A of plot 32 shows how the illustrated knee flexor muscles areactive during the time associated with region 28B.

In some embodiments of the invention, methods and apparatus are providedfor selectively harvesting energy from the movement of particular jointswhen the muscles associated with the particular joints are operating innegative mechanical power modes 20 (i.e. when muscles would normally beactive to decelerate movement of the joints). Selectively harvestingenergy from the movement of particular joints when the musclesassociated with the particular joints are operating in a negativemechanical power mode 20 is referred to herein as “mutualistic” energyharvesting. In particular embodiments, the harvested energy is output aselectrical power. The term mutualistic is appropriate because themechanical power used to generate electric power under mutualisticconditions can come from the decelerating joints and the harvesting ofenergy under mutualistic conditions actually assists the muscles todecelerate the joints.

FIG. 3B schematically illustrates mutualistic energy harvesting 40 whenmuscle 12 is operating in a negative mechanical power mode 20. Asdiscussed above in relation to FIG. 1B, when muscle 12 is operating innegative mechanical mode 20, muscle 20 consumes metabolic (chemical)energy in an effort to reduce the mechanical energy of one or moreassociated body segment(s) 44 (i.e. cause body segment 44 to decelerate)and outputs heat energy during this process. As shown in FIG. 3B, whenharvesting energy in a mutualistic manner 40, a harvester 42 helps toreduce the mechanical energy of associated body segment 44 (i.e. causebody segment 44 to decelerate) by converting the mechanical energy ofassociated body segment 44 into electrical energy. Rather than usingenergy from muscle 12 alone to cause body segment 44 to decelerate,harvester 42 helps to cause body segment 44 to decelerate and in doingso converts mechanical energy to electrical energy.

Accordingly, mutualistic energy harvesting may actually decrease themetabolic costs associated with decelerating the motion of body segment44. Harvester 42 may comprise a generator, for example, and themechanical energy required to turn the generator may be obtained frommovement of associated body segment 44 as it decelerates.

When selectively harvesting energy in a mutualistic mode 40, muscle 12requires less metabolic (chemical) energy, because part of the negativepower required to cause body segment 44 to decelerate is provided byharvester 42. Accordingly, selectively harvesting energy in amutualistic mode 40 can actually reduce the metabolic cost and/or effortnormally experienced by a person when performing an activity. Forexample, assuming that harvester 42 has a 50% mechanical to electricalconversion efficiency, then extracting 1 W of electrical power fromharvester 42 would require 2 W of mechanical energy, meaning that themechanical energy reduction performed by muscle 12 would be 2 W less.Assuming that muscle 12 operates with the above-discussed −120%efficiency in negative mechanical power mode 20, then a 2 W reduction inmechanical energy corresponds approximately to a 1.7 W reduction inmetabolic (chemical) energy consumed by muscle 12.

In some embodiments, energy harvesting methods and apparatus alsoharvest energy from the movement of particular joints when the musclesassociated with the particular joints are operating in positivemechanical power modes 10 (i.e. when muscles are active to generatemovement of the body). Harvesting energy from the movement of particularjoints when the muscles associated with the particular joints areoperating in a positive mechanical power mode 20 is referred to hereinas “non-mutualistic” energy harvesting. Non-mutualistic energyharvesting generally requires increased metabolic costs (i.e. chemicalenergy) from the muscles. For this reason, non-mutualistic energyharvesting may also be referred to as “parasitic” energy harvesting.

FIG. 3A schematically illustrates non-mutualistic energy harvesting 50when muscle 12 is operating in a positive mechanical power mode 10. Asdiscussed above in relation to FIG. 1A, when muscle 12 is operating inpositive mechanical mode 10, muscle 20 consumes metabolic energy in aneffort to generate mechanical energy in one or more associated bodysegment(s) 44 (i.e. to cause body segment(s) 44 to move) and outputsheat energy during this process. As shown in FIG. 3A, when harvestingenergy in a non-mutualistic manner 50, harvester 42 requires additionalmechanical energy generated by muscle 12 and associated with movement ofbody segment 44 to provide electrical energy. In contrast to mutualisticenergy harvesting 40, non-mutualistic energy harvesting 50 requires thatthe user work harder (i.e. to exert more effort) in order to generateelectrical energy. For example, assuming that harvester 42 has a 50%mechanical to electrical conversion efficiency, then extracting 1 W ofelectrical power from harvester 42 would require 2 W of mechanicalenergy, meaning that muscle 12 would have to provide an additional 2 Wof mechanical energy. Assuming that muscle 12 operates with theabove-discussed 25% efficiency in positive mechanical power mode 10,then a 2 W increase in mechanical energy production corresponds to an 8W increase in the metabolic (chemical) energy consumed by muscle 12. Theincreased metabolic cost and/or effort of non-mutualistic energyharvesting relative to mutualistic energy harvesting tends to limit themaximum power available from non-mutualistic energy harvesting and theduration over which energy can be harvested.

In some embodiments where it is desired to harvest energymutualistically, methods and apparatus are provided which incorporateone or more feedback-providing sensors. Feedback from such sensors canbe used to make decisions as to whether particular muscle(s) is/areoperating in a negative mechanical power mode 20, thus permittingselective engagement and disengagement of the generator for mutualisticenergy harvesting 40 and for avoiding, to the extent possible,non-mutualistic energy harvesting 50.

In some embodiments, methods and apparatus are provided for selectivemutualistic energy harvesting of the energy associated with knee motionwhen a person is walking. As discussed above in relation to typicalwalking cycle 21 of FIG. 2, each walking cycle involves:

-   -   a period of time (region 28A) near the beginning of stance phase        21A, where the knee is flexing as the weight of the body is        being transferred to the corresponding leg and the knee extensor        muscles operate in a negative mechanical power mode to receive        this weight and decelerate this flexion; and    -   a period of time (region 28B) near the end of swing phase 21B,        where the knee is extending and the knee flexor muscles operate        in a negative mechanical power mode to decelerate this flexion.

As illustrated in FIG. 2, substantial power may be available in regions28A, 28B at normal walking speeds. This available power will tend toincrease for a heavier person or when a person is walking faster or whena person is walking downhill.

FIG. 2 also shows another region 28D at the end of stance phase 21A andthe beginning of swing phase 21B, where the knee is flexing and exhibitsnegative power. However, it can be seen from plot 30, that theillustrated knee extensor muscles are not active during the timeassociated with region 28D. Those skilled in the art will appreciatethat region 28D represents a period of positive mechanical poweroperation with the muscles associated with the ankle (i.e. movement ofthe ankle). Some of the ankle muscles (e.g. the gastrocnemius) cross theknee joint. A potential consequence of harvesting energy from knee jointmotion in region 28D is interference with the positive mechanical poweroperation of these muscles with respect to the ankle joint. Harvestingenergy in region 28D may be non-mutualistic because of the increase inmetabolic cost associated with interfering with the positive poweroperational mode of the muscles that cross both the ankle and kneejoints. In general, it is desirable to consider the function ofindividual muscles when considering whether to harvest energy.

FIGS. 4A, 4B and 4C depict a number of different exemplary embodimentsof the invention. FIG. 4A shows a wearable energy harvesting apparatus60 according to a particular embodiment of the invention. In theillustrated embodiment, harvesting apparatus 60 operates to harvestenergy from the motion of knee joint 62 and the corresponding kneeextensor muscles and knee flexor muscles. FIG. 4B shows an energyharvesting apparatus 70 according to another embodiment of the inventionthat is embedded in a prosthetic limb 74. In the illustrated embodiment,prosthetic limb 74 incorporates a joint 72 which is intended to emulatea knee joint. In the illustrated embodiment, harvesting apparatus 70operates to harvest energy from the motion of joint 72. FIG. 4C shows anenergy harvesting apparatus 80 according to yet another embodiment ofthe invention that is implanted under the skin of the host to harvestenergy from the motion of ankle joint 82 and its corresponding ankleflexor and extensor muscles (e.g. the tibialis anterior).

Energy harvesting apparatus 60 (FIG. 4A) can be mounted to and/or wornon the body 61 of a human. In the illustrated embodiment, apparatus 60is mounted across knee joint 62 with an upper component 64 located aboveknee joint 62, a lower component 66 located below knee joint 62 and apivot joint 68 located generally coaxially with knee joint 62. When thehost (i.e. the person to whom apparatus 60 is mounted) bends knee joint62, pivot joint 68 pivots allowing corresponding relative movementbetween upper component 64 and lower component 66. Energy harvester 60may be designed to harvest energy during extension of knee joint 62,during flexion of knee joint 62 or during both extension and flexion. Inother embodiments, energy harvesting apparatus can be configured to bemounted across other joints, such as the ankle, wrist or elbow, forexample. In other embodiments, energy harvesting apparatus may extendacross a plurality of joints, such as the knee and the ankle or theelbow and the shoulder for example.

FIG. 5A is a schematic block diagram of energy harvesting apparatus 60according to a particular embodiment of the invention. Energy harvestingapparatus 60 comprises a transmission 102 which is mechanicallyconnected to the body 61 of a host via a mechanical connection 100. Inthe illustrated embodiment, connection 100 connects the knee 62 of thehost to transmission 102. Connection 100 transfers mechanical power(represented by line 112) from knee 62 to transmission 102. Connection100 may comprise one or more of upper and lower components 64, 66 andpivot joint 68 (see FIG. 4A). In other embodiments, connection 100 maybe provided by other suitably configured mechanisms. Transmission 102transforms mechanical power 112 received from connection 100 into adifferent form of mechanical power (represented by line 114) suitablefor use by generator 104. In some embodiments, transmission 102 convertsrelatively high-torque, low-speed mechanical power (e.g. the type ofmechanical power produced by knee joint 62) into relatively low-torque,high-speed mechanical power which is suitable for use by generator 104.

Generator 104 converts mechanical power 114 into electrical power signal116. Depending on the nature of mechanical power input 114 and generator104, electrical power signal 116 may have a variety of forms.Accordingly, in the illustrated embodiment, energy harvesting apparatus60 comprises a signal conditioner 106 which conditions electrical powersignal 116 to generate an electrical power output signal 118. Electricalpower output signal 118 output by signal conditioner 106 is supplied toan electrical load 111. Electrical load 111 may comprise any one or morecomponents capable of using and/or storing electrical power from outputsignal 118. Non-limiting examples of suitable electric loads 111 includeelectronic devices (e.g. personal electronic devices) and batterychargers.

Energy harvester 60 also comprises a controller 108 which receives afeedback signal 122 from one or more sensors 110. Controller 108 maycomprise one or more data processors, together with suitable hardware,including, by way of non-limiting example: accessible memory, logiccircuitry, drivers, amplifiers, A/D and D/A converters and the like.Controller 108 may comprise, without limitation, a microprocessor, acomputer-on-a-chip, the CPU of a computer or any other suitablemicrocontroller. Controller 108 may comprise a plurality of dataprocessors.

Feedback signal 122 preferably provides controller 108 with informationthat may be used by controller 108 to determine whether or notconditions are suitable for mutualistic energy harvesting. Sensor(s) 110may comprise a wide variety of sensors and may detect, by way ofnon-limiting example, positions of the body of the host (e.g. one ormore limbs or other body segments), positions and/or activity levels ofmuscles, positions and/or configurations of generator 104, transmission102 and/or connection 100. Non-limiting examples of sensor(s) which maybe suitable for sensor(s) 110 include potentiometers, accelerometers,rate gyroscopes, position encoders, inclinometers, pressure sensors orthe like that detect contact of a body segment with another object (e.g.the ground). Sensor(s) 110 may comprise signal conditioning circuitry(not shown) that is well known to those skilled in the art for providinga signal suitable for use by controller 108. By way of non-limitingexample, such circuitry may comprise amplifiers, analog to digital A/Dconverters, filters and the like.

Controller 108 may make use of the information contained in feedbacksignal 122 to determine whether or not conditions are suitable formutualistic energy harvesting. In some embodiments, controller 108 isconfigured, or may be configured (e.g. by user input), to causeharvester 60 to harvest energy primarily under conditions considered bycontroller 108 to be mutualistic. In such embodiments, controller 108couples body 61 (e.g. knee 62) to electrical load 111 under conditionswhich controller 108 determines to be mutualistic and disengages body 61(e.g. knee 62) from electrical load 111 under conditions whichcontroller 108 determines to be non-mutualistic.

Controller 108 may use a wide variety of techniques to couple body 61 toelectrical load 111 under mutualistic conditions and/or decouple body 61from electrical load 111 under non-mutualistic conditions. Techniquesfor coupling body 61 to, and decoupling body 61 from, load 111 caninvolve mechanical coupling/decoupling. For example, controller 108 mayuse signal 120A to cause connection 100 to be mechanically coupled tobody 61 under mutualistic conditions and to cause connection 100 to bemechanically decoupled from body 61 under non-mutualistic conditions.Controller 108 may additionally or alternatively use signal 120A and/orsignal 120B to control the operation of connection 100 and/ortransmission 102, such that connection 100 and transmission 102 aremechanically coupled to one another under mutualistic conditions and aremechanically decoupled from one another under non-mutualisticconditions. Controller 108 may additionally or alternatively use signal120B and/or signal 120C to control the operation of transmission 102and/or generator 104, such that transmission 102 and generator 104 aremechanically coupled to one another under mutualistic conditions and aremechanically decoupled from one another under non-mutualisticconditions. By way of non-limiting example, such mechanical coupling anddecoupling (e.g. between connection 100 and transmission 102 and/orbetween transmission 102 and generator 104) may be accomplished using asuitably configured clutch which is responsive to one or more of signals120A, 120B, 120C or a suitably configured locking mechanism that isresponsive to one or more of signals 120A, 120B, 120C.

In embodiments where it is desired to harvest energy primarily underconditions considered by controller 108 to be mutualistic, controller108 may additionally or alternatively use electrical coupling/decouplingmechanisms for coupling body 61 to, and decoupling body 61 from, load111. For example, controller 108 may use signal 120C and/or signal 120Dto electrically connect generator 104 to conditioning circuitry 106under mutualistic conditions and to electrically disconnect generator104 from conditioning circuitry 106 under non-mutualistic conditions.Controller 108 may additionally or alternatively use signal 120D toelectrically connect conditioning circuitry 106 to electrical load 111under mutualistic conditions and to electrically disconnect conditioningcircuitry 106 from electrical load 111 under non-mutualistic conditions.By way of non-limiting example, such electrical coupling and decoupling(e.g. between generator 104 and conditioning circuitry 106 and/orbetween conditioning circuitry 106 and load 111) may be accomplishedusing a suitably configured electrical switch which is responsive to oneor more of signals 120C, 120D.

In some embodiments, controller 108 is configured, or may be configured(e.g. by user input), to cause harvesters 60 to harvest energy undermutualistic and non-mutualistic conditions. Where it is desired tocontinually harvest energy under mutualistic and non-mutualisticconditions, controller 108 and sensors 110 are not generally required.In some embodiments, signals 120A, 120B and/or 120C may be used bycontroller 108 to control other aspects of the operation of connection100, transmission 102 and/or generator 104. Controller 108 may alsooptionally control the operation of signal conditioner 106 using signal120D. In the illustrated embodiment, signals 120A, 120B, 120C, 120Dcomprise one way signals, but, in other embodiments, signals 120A, 120B,120C, 120D comprise two-way signals.

In some embodiments, controller 108 is configured, or may be configured(e.g. by user input), to turn off harvester 60 (i.e. so that harvester60 stops harvesting activity altogether until it is activated again).

FIG. 5B is a schematic block diagram showing a method 45 for determiningwhen to engage the FIG. 5A energy harvesting apparatus to harvest energyunder mutualistic conditions according to a particular embodiment of theinvention. Method 45 begins in block 47 where controller 108 obtainsfeedback 122 from sensor(s) 110. As discussed above, controller 108makes use of feedback data 122 (which may include present and historicalfeedback data 122) to make a decision as to whether conditions aremutualistic such that energy should be harvested. In block 49, method 45involves processing feedback data 122. The block 49 processing maycomprise filtering, scaling, offsetting or otherwise digitallymanipulating the incoming angular position data, for example. In someembodiments, some of the block 49 processing may occur in the analogdomain (i.e. prior to the block 47 data acquisition).

Method 45 then proceeds to block 51 which involves an inquiry intowhether or not controller 108 considers the conditions to bemutualistic. In some embodiments, the block 51 inquiry comprisesconsidering a model of the motion associated with one or more joints(e.g. knee 62) and using the model together with measuredcharacteristics associated with the one or more joints (e.g. feedbackdata 122) to determine whether conditions are mutualistic. In someembodiments, the block 51 inquiry additionally or alternativelycomprises direct measurement or sensing of muscle activity to determinewhether conditions are mutualistic. The block 51 inquiry may compriseassessing whether: (i) one or more muscles associated with the one ormore joints are acting to decelerate motion of the one or more joints;(ii) one or more muscles associated with the one or more joints areproducing torque in a particular direction and the one or more jointsare moving in the opposing direction; (iii) one or more musclesassociated with the one or more joints are extending and the same one ormore muscles are active; and/or (iv) one or more muscles associated withthe one or more joints are otherwise operating in a negative mechanicalpower operational mode.

The block 51 inquiry may also involve an optional inquiry into whetherthere is some reason that controller 108 should not cause energy to beharvested even though conditions appear to be mutualistic. Such aninquiry may involve knowledge of particular types of movement of the oneor more joints and/or the one or more associated muscles. By way ofexample, controller 108 may determine, during such an inquiry, that itis not desirable to harvest energy from knee 62 during region 28D of thewalking cycle (see FIG. 2) even though one or more muscles associatedwith knee 62 are operating in a negative mechanical power operationalmode. As discussed above, negative power operation of some musclesassociated with knee motion in region 28D may be accompanied by positivepower operation of the same muscles associated with ankle motion.

If controller 108 determines in block 51 that conditions are mutualistic(block 51 YES output), then method 45 proceeds to block 53 wherecontroller 108 causes an appropriate one or more of signals 120A, 120B,120C, 120D to couple body 61 to electrical load 111, thereby engagingenergy harvesting. If controller 108 determines in block 51 thatconditions are non-mutualistic (block 51 NO output), then method 45proceeds to block 55 where controller 108 causes an appropriate one ormore of signals 120A, 120B, 120C, 120D to decouple body 61 fromelectrical load 111, thereby disengaging energy harvesting. Method 45then loops back to block 47.

FIGS. 6A, 6B, 7 and 8 show an energy harvester 60A according to anotherembodiment of the invention. In many respects, energy harvester 60A issimilar to energy harvester 60 described above and similar referencenumerals are used to describe features of energy harvester 60A that aresimilar to corresponding features of energy harvester 60. Like energyharvester 60, energy harvester 60A is connected to knee 62 of the hostby connection 100. Energy harvester 60A is configured to harvest energyassociated with extension of knee 62 only. In addition, as discussedfurther below, energy harvester 60A is configurable to selectivelyharvest energy under mutualistic conditions when the knee flexor musclesare operating in negative mechanical power mode to decelerate theextension motion of knee 62.

Energy harvester 60A comprises a connection 100 which transfersmechanical power 112 from knee 62 to transmission 102. As shown in FIGS.6A, 6B and 7, connection 100 of energy harvester 60A comprises an uppercomponent 64 located above knee 62 and a lower component located belowknee 62 which are coupled to one another by a pivot joint 68 that isgenerally coaxial with knee joint 62. In the illustrated embodiment,connection 100 also comprises upper band 64A which couples uppercomponent 64 to thigh 67 of the host and lower band 66A which coupleslower component 66 to calf 69 of the host. Upper band 64A and lower band66A may be provided by a single component similar to a orthopedic kneebrace, for example. The positions of upper band 64A and lower band 66Amay be adjusted upwardly and downwardly (i.e. toward and/or away fromknee joint 62) to adjust the coupling between the host and energyharvester 60A. Preferably, connection 100 is designed to have a minimalimpact on the available range of motion of knee joint 62.

In the illustrated embodiment, connection 100 comprises a torquetransfer shaft 131, such that movement of pivot joint 68 in eitherdirection causes corresponding movement of shaft 131. Rotation of torquetransfer shaft 131 is schematically represented in FIG. 8 by line 112.

Transmission 102 of energy harvester 60A converts relativelyhigh-torque, low-speed mechanical power 112 (e.g. the type of mechanicalpower produced by knee joint 62 (see torque plot 26 of FIG. 2)) intorelatively low-torque, high-speed mechanical power 114 which is suitablefor use by generator 104. In the illustrated embodiment, transmission102 of energy harvester 60A comprises a roller clutch 130 and a geartrain 134.

As discussed above, energy harvester 60A only harvests energy associatedwith the extension of knee joint 62. This functionality is provided byroller clutch 130 which comprises a mechanical bypass 132. Roller clutch130 is a uni-directional torque transfer mechanism. When shaft 131rotates in a particular direction corresponding, in this embodiment, toextension of knee joint 62, roller clutch 130 engages shaft 131, therebycausing rotation of roller clutch 130 and corresponding rotation ofgearing 134. Conversely, when shaft 131 rotates in the opposingdirection corresponding, in this embodiment, to flexion of knee joint62, mechanical bypass 132 allows shaft 131 to rotate freely relative toroller clutch 130. The intermittent rotation of roller clutch 130(corresponding to extension of knee joint 62) causes correspondingintermittent rotation of gearing 134 with relatively high-torque andrelatively low-speed. The intermittent rotation of roller clutch 130 isrepresented in FIG. 8 by line 142.

The intermittent rotation of shaft 131 (mechanical power 142) istransferred to gearing mechanism 134. Gearing mechanism 134 has arelatively high input to output gear ratio, so that relativelyhigh-torque, low-speed mechanical power 142 is converted to relativelyhigh-speed, low-torque mechanical power (represented in FIG. 8 by line114). In particular embodiments, the input to output gearing ratio ofgearing mechanism 134 may be in a range of 25-500. Relativelyhigh-speed, low-torque mechanical power 114 output by gearing mechanism134 is preferably configured (by gearing mechanism 134) to providemechanical power suitable for input to generator 104. Gearing mechanism134 is preferably relatively lightweight and not overly cumbersome. Inother embodiments, the torque/speed conversion function of gearingmechanism 134 is implemented by other transmission systems andcombinations of transmission systems, such as belt and pulley-basedtransmission systems, rack and pinion-based transmission systems and thelike, for example.

Mechanical power 114 is received by generator 104. In general, generator104 can comprise any suitable generator capable of converting mechanicalpower 114 into electrical power 116. Preferably, generator 104 isrelatively lightweight and is not overly cumbersome. In one particularembodiment, generator 104 comprises a rotary-magnetic brushless DC motorwhich outputs three phase electrical output power 116. Those skilled inthe art will appreciate that there are a relatively large variety ofgenerators capable of converting mechanical power 114 into electricalpower 116. In general, generator 104 may comprise any suitablyconfigured generator.

In the illustrated embodiment, energy harvester 60A comprises a signalconditioner 106. Signal conditioner 106 functions generally to conditionelectrical power signal 116 output from generator 104 to a form suitablefor use by electrical load 111. Accordingly, signal conditioner 106 maytake a wide variety of forms and may comprise a wide variety ofcomponents, depending on the particulars of generator 104 (and itsoutput power signal 116) and depending on the nature of electrical load111 and its input requirements.

In the illustrated embodiment, generator 104 comprises a rotary-magneticbrushless DC motor which outputs a three phase electrical power signal116 and electrical load 111 comprises a rechargeable DC battery whichrequires a single-phase electrical input signal 118. In the illustratedembodiment, to provide this multi-phase to single-phase conversion,signal conditioner 106 comprises a full wave rectifier 138 andassociated power conditioning circuitry 140. Power conditioningcircuitry 140 may comprise one or more filters to reduce the ripplevoltage of signal 146 output from rectifier 138 before providingelectrical power output 118 to electrical load 111.

In the illustrated embodiment, signal conditioner 106 also comprises aswitch 136, which is controlled by signal 120D from controller 108. Whenswitch 136 is closed, electrical power signal 116 from generator 104 istransmitted to rectifier 138. However, when switch 136 is open,generator 104 is open circuited such that electrical power signal 116does not reach rectifier 138. In this manner, when switch 136 is open,electrical load 111 is decoupled from the motion of knee 62 and theresistance to knee motion is reduced. Switch 136 may generally compriseany switch that is controllable by signal 120D (e.g. solid stateswitches, electro-mechanical switches or the like). In one particularembodiment, switch 136 comprises the AQZ202 switch manufactured byPanasonic Corporation.

As discussed above, energy harvester 60A is configurable such that itharvests energy under mutualistic conditions. To achieve this objective,controller 108 uses feedback signal 122 from sensor(s) 110 to determinewhether or not conditions are suitable for mutualistic energyharvesting. When controller 108 determines that conditions are suitablefor mutualistic energy harvesting, controller 108 sends a signal 120Dwhich causes switch 136 to be closed and electrical signal 116 fromgenerator 104 to be received by rectifier 138. Conversely, whencontroller 108 determines that conditions are not suitable formutualistic energy harvesting, controller 108 sends a signal 120D whichcauses switch 136 to open, thereby decoupling electrical load 111 fromthe motion of knee 62.

In this manner, controller 108 uses signal 120D to control switch 136thereby causing energy harvester 60A to selectively harvest energy undermutualistic conditions.

In the illustrated embodiment, switch 136 represents a means forselectively coupling the movement of knee 62 to, and decoupling themovement of knee 62 from, electrical load 111 in response to a signalfrom controller 108. As discussed above in relation to energy harvester60, energy harvester 60A may additionally or alternatively comprise anumber of different means for selectively coupling the movement of knee62 to, and decoupling the movement of knee 62 from, electrical load 111in response to a signal from controller 108. Such means may compriseelectrical means, mechanical means and/or electro-mechanical means andsuch means may be located at various places within energy harvester 60A.

To selectively harvest energy under mutualistic conditions, controller108 uses feedback signal 122 from sensor(s) 110 to make a decision aboutwhether or not current operating conditions are mutualistic. In oneparticular embodiment, controller 108 is configured to implementmodel-based control. For example, when knee 62 is being used in arepetitive manner (e.g. when walking, running or performing knee bends),the movement of knee 62 can be predicted relatively accurately based ona model. Such a model may comprise a known model corresponding to therepetitive movement (e.g. a known model relating to human walkingpatterns or human knee bend patterns or human cycling patterns). Such amodel may be constructed from previous measurements on the host or onone or more other subjects, for example. Those skilled in the art willappreciate that there are a number of ways in which suitable modelscould be constructed. Controller 108 can be programmed or otherwiseconfigured with information relating to one or more models and can usesuch model(s) in conjunction with feedback signal 122 from sensor(s) 110to predict whether or not current operating conditions are mutualistic.

In the illustrated embodiment of FIGS. 6A, 6B, 7 and 8, controller 108of energy harvester 60A makes use of such model-based control todetermine when conditions are mutualistic. As discussed above, energyharvester 60A is configured to harvest energy associated with themovement of knee 62 in the extension direction only. When the host iswalking, plots 24, 26, 28 and 32 (FIG. 2) show that region 28Brepresents a time where: (i) knee 62 is extending (indicated by anangular velocity (plot 24) greater than zero); and (ii) the knee flexormuscles are operating in a negative mechanical power mode to deceleratethe extension motion of knee 62 (i.e. conditions aremutualistic—indicated by plot 28 being less than zero and plot 32showing a high level of activity of the knee flexor muscles and alsoindicated by torque (plot 26) and angular velocity (plot 24) havingopposite signs). Accordingly, region 28B represents an ideal time forenergy harvester 60A to harvest energy. When energy harvester 60Aharvests energy in region 28B, the mechanical power required to turngenerator 104 actually assists the knee flexor muscles to decelerate theextension of knee 62 (i.e. reducing the effort and/or metabolic costassociated with decelerating the extension of knee 62).

As discussed above, controller 108 makes use of feedback signal 122 tohelp make the decision as to whether conditions are mutualistic. In theillustrated embodiment of FIGS. 6A, 6B, 7 and 8, sensor(s) 110 of energyharvester 60A comprise a potentiometer 113, which produces a feedbacksignal 122 representative of the angular position of knee 62. It will beappreciated by those skilled in the art that other types of sensorscould be used to provide this angular position feedback signal 122 orsimilar information about the angular characteristics of knee 62. Suchother types of sensors may include optical encoders, magnetic encoders,mechanical encoders, accelerometers and/or rate gyroscopes for example.

FIG. 9 is a block diagram illustrating a method 200 for predicting theexistence of mutualistic conditions and for harvesting energy duringsuch mutualistic conditions and disengaging energy harvesting whenconditions are non-mutualistic. Method 200 is suitable for use withenergy harvester 60A of FIGS. 6A, 6B, 7 and 8. Those skilled in the artwill appreciate, however, that method 200 may be modified for use withother embodiments. FIG. 10 shows a number of plots relating to theharvesting of energy while the host is walking using energy harvester60A in accordance with method 200. Characteristics of the FIG. 10 plots(e.g. the amplitude and frequency) may vary for each individual host andfor the conditions being experienced by a particular host.

As discussed above, walking is a relatively repetitive motion. Plot 220shows the angle of knee joint 62 of a particular host during a walkingmotion. As discussed above, controller 108 may determine the angle ofknee joint 62 using feedback signal 122 from sensor(s) 110 (i.e.potentiometer 113 in the illustrated embodiment). When the host iswalking, each cycle 21 of plot 220 comprises a stance phase 21A and aswing phase 21B. Plot 223 shows the angular velocity of knee joint 62.The angular velocity plot 223 may be obtained by taking the derivativeof the angular position plot 220, for example.

Method 200 of FIG. 9 makes use of model-based control. In theillustrated embodiment, method 200 also makes use of sensor(s) whichprovide information relating to the angular position or other angularcharacteristics of knee 62. In alternative embodiments, method 200 maymake use of other sensors that detect one or more characteristicsassociated with a repetitive motion (e.g. walking). By way ofnon-limiting example, such other sensors may comprise pressure sensors,which detect heel strike.

Method 200 begins in block 202, where controller 108 reads feedbacksignal 122 from angular position sensors 110. In block 204, controller108 processes the newly acquired sensor information. The block 204processing may comprise filtering, scaling, offsetting or otherwisedigitally manipulating the incoming angular position data, for example.In some embodiments, some of the block 204 processing may occur in theanalog domain. In the particular embodiment of method 200, block 204comprises taking a derivative of the incoming angular position data toobtain data representative of the angular velocity.

Block 206 involves an inquiry into whether the processed sensor dataindicates that knee 62 has just begun the swing phase knee extension.The swing phase knee extension is shown as region 22E of plot 22 (FIG.2). In one particular embodiment, the block 206 inquiry involves aninquiry into whether:

-   -   (i) the angular velocity crosses zero from a negative value to a        positive value (i.e. the angular velocity crosses zero with a        positive slope); and    -   (ii) the angular position is lower than a threshold value        (φ_(thresh)).

An angular velocity zero crossing with a positive slope is indicative ofa transition from flexion toward extension. However, as shown in FIG.10, within each walking cycle 21, there are two such transitions 227Aand 227B, where the angular velocity exhibits a zero crossing with apositive slope. The angular position being lower than a threshold value(φ_(thresh)) can be used to indicate that the particular positive-slopedzero crossing of the angular velocity being detected represents thebeginning of the swing phase knee extension. As shown in FIG. 10, thepositive-sloped angular velocity zero crossing associated withtransition 227A has an associated angular position greater than thethreshold value (φ_(thresh)), meaning that the positive-sloped angularvelocity zero crossing associated with transition 227A does notcorrespond with the swing phase knee extension. On the other hand, thepositive-sloped angular velocity zero crossing associated withtransition 227B has an associated angular position that is less than thethreshold value (φ_(thresh)), meaning that the positive-sloped angularvelocity zero crossing associated with transition 227B represents thebeginning of the swing phase knee extension.

Those skilled in the art will appreciate that there are other techniqueswhich may be used to predict the beginning of the swing phase kneeextension in block 206. For example, it is not strictly necessary todetect that the angular velocity zero crossing has a positive slope. Inthe illustrated example associated with walking (FIG. 10), controller108 may conclude that the beginning of the swing phase knee extensionoccurs whenever the angular velocity crosses zero and the angularposition is less than the threshold value (φ_(thresh)). In otherembodiments, controller 108 may make use of acceleration data (i.e. bytaking a second derivative of the angular position data or by directlydetecting acceleration data) to assist with determining the beginning ofthe swing phase knee extension. It will be appreciated by those skilledin the art, that zero acceleration represents the transition from stancephase 21A to swing phase 21B (FIG. 10). In still other embodiments,sensors may be provided to detect other characteristics associated withrepetitive motion and such other characteristics may be used to assistwith determining the beginning of the swing phase knee extension. By wayof non-limiting example, a pressure sensor placed on the foot may beused to detect the transition from stance phase 21A to swing phase 21B.If the start of the swing phase is known (e.g. using an accelerometer ora foot pressure sensor), a delay may be used as a basis for predictingthe start of the swing phase knee extension. Such a delay may be basedon the frequency of the repetitive motion, for example.

If the block 206 inquiry indicates that the swing phase knee extensionhas just begun (block 206 YES output), then method 200 proceeds to block210 where a short delay occurs before method 200 proceeds to block 212.The amount of the block 210 delay may be constant or variable. The block210 delay may be separately configured (or configurable) for each user.The block 210 delay may be related to the period of the walking cycle 21of a particular host or to the slope of the terrain. The block 210 delaymay be adaptive. By way of non-limiting example, if the period of thewalking cycle changes or the slope of the terrain changes, then theblock 210 delay may change accordingly. The block 210 delay may beconfigured to achieve improved performance (e.g. greater power outputand/or improved user comfort). In some cases, the block 210 delay can beset to zero. In block 212, controller 108 outputs signal 120D whichcauses switch 136 to enter its closed state, where generator 104 iscoupled to electrical load 111 and energy harvesting commences. Method200 then loops back to block 202, where controller 108 obtains moreangular position data from sensors 110.

Plot 222 of FIG. 10 represents control signal 120D which, in theillustrated embodiment, is a binary signal having an enable harvestlevel and a disable harvest level. Block 212 corresponds to a transitionof control signal 120D from its disable harvest level to its enableharvest level. In response to this transition of control signal 120D,switch 136 is closed and the motion of knee 62 is coupled to electricalload 111, such that electrical power output signal 118 is delivered toload 111.

The next time method 200 arrives at block 206, the swing phase kneeextension will have begun on the previous loop, so method 200 will exitblock 206 through the block 206 NO output into block 208. In general,block 208 involves determining whether the energy harvesting engaged inblock 212 should be discontinued (e.g. because conditions are no longermutualistic). If energy harvesting is engaged at (or near) the beginningof the swing phase knee extension region 22E of plot 22 (FIG. 2), thenit should be discontinued prior to the commencement of stance phase kneeextension region 22B of plot 22 (FIG. 2). Even if switch 136 is closed,energy harvesting will not occur in region 22A of plot 22 (FIG. 2), asknee 62 is flexing and roller clutch 130 acts to decouple knee 62 fromgenerator 104. Accordingly, in the illustrated embodiment, the block 208inquiry into whether the energy harvesting engaged in block 212 shouldbe discontinued comprises an inquiry into whether the processed sensordata indicates that knee 62 has just begun the stance phase kneeextension.

As shown in FIG. 10, commencement of the stance phase knee extensioncorresponds with the positive-sloped angular velocity zero crossingassociated with transition 227A. In one particular embodiment, the block208 inquiry involves an inquiry into whether:

-   -   (i) the angular velocity crosses zero from a negative value to a        positive value (i.e. the angular velocity crosses zero with a        positive slope); and    -   (ii) the angular position is greater than the threshold level        (φ_(thresh)).

Those skilled in the art will appreciate that there are other techniqueswhich may be used to predict the beginning of the stance phase kneeextension in block 208. For example, it is not strictly necessary todetect that the angular velocity zero crossing has a positive slope. Inthe illustrated example associated with walking (FIG. 10), controller108 may conclude that the beginning of the stance phase knee extensionoccurs whenever the angular velocity crosses zero and the angularposition is greater than the threshold value (φ_(thresh)). In otherembodiments, controller 108 may make use of acceleration data (i.e. bytaking a second derivative of the angular position data or by directlydetecting acceleration data) to assist with determining the beginning ofthe swing phase knee extension. It will be appreciated by those skilledin the art, that zero acceleration represents a minimum of the angularvelocity that precedes the stance phase knee extension (see FIGS. 2 and10). In still other embodiments, sensors may be provided to detect othercharacteristics associated with repetitive motion and such othercharacteristics may be used to assist with determining the beginning ofthe swing phase knee extension. By way of non-limiting example, apressure sensor placed on the foot may be used to detect the transitionfrom swing phase 21B to stance phase 21A. If either of these conditions(e.g. the angular velocity minimum that precedes the stance phase kneeextension or the beginning of the stance phase), a delay may be used asa basis for predicting the start of the stance phase knee extension.Such a delay may be based on the frequency of the repetitive motion, forexample.

If the block 208 inquiry indicates that stance phase knee extension hasnot just begun (block 208 NO output) and switch 136 is closed (i.e.energy harvester 60A is harvesting energy), then switch 136 remainsclosed and energy harvester 60A continues to harvest energy while method200 loops back to block 202. If on the other hand, the block 208 inquiryindicates that the stance phase knee extension has just begun (block 208YES output) and switch 136 is closed (i.e. energy harvester 60A isharvesting energy), then method 200 proceeds to block 214 where a shortdelay occurs before method 200 proceeds to block 216. The amount of theblock 214 delay may be constant or variable. The block 214 delay may beseparately configured (or configurable) for each user. The block 214delay may be related to the period of the walking cycle 21 of aparticular host or the slope of the terrain on which the host iswalking. The block 214 delay may be adaptive. By way of non-limitingexample, if the period of the walking cycle or the slope of the terrainchanges, then the block 214 delay may change accordingly. The block 214delay may be configured to achieve improved performance (e.g. greaterpower output and/or improved user comfort). In some cases, the block 214delay can be set to zero.

In block 216, controller 108 outputs signal 120D which causes switch 136to enter its open state, where generator 104 is decoupled fromelectrical load 111 and energy harvesting is discontinued. Block 216comprises a transition of control signal 120D (plot 222 of FIG. 10) fromits enable harvest level to its disable harvest level. In response tothis transition of control signal 120D, switch 136 is opened and themotion of knee 62 is decoupled from electrical load 111. After block216, method 200 again loops back to block 202.

If the block 208 inquiry indicates that stance phase knee extension hasnot just begun (block 208 NO output) and switch 136 is open (i.e. energyharvester 60A is not harvesting energy), then method 200 loops back toblock 202 without changing the status of switch 136.

Plot 224 represents the instantaneous power of electrical power outputsignal 118. It can be seen by comparing plot 224 and plot 222 thatelectrical power is only harvested when control signal 120D (plot 220)is at its enable harvest level. As discussed above, control signal 120Dis at its enable harvest level during the swing phase knee extension,when the knee flexor muscles are acting in a negative mechanical powermode to decelerate the extension of knee 62 and conditions aremutualistic. Plot 226 represents the average power of electrical poweroutput signal 118 (i.e. the average of plot 224). In the particularexample shown in FIG. 10, harvester 60A generates an average power of2.4 W when the host is walking.

In other embodiments, model-based control similar to that of FIGS. 9 and10 may be used for other cyclical movements. Non-limiting examples ofsuch cyclical movements include: running, jumping, knee bends, climbing,ascending and/or descending stairs or embankments, and the like.

In another embodiment, controller 108 is configured to directly sensemuscle activity to help determine when conditions are mutualistic. Insuch muscle activity-based control, sensors 110 may comprise one or moreposition sensors for sensing the angle of a joint or other angularcharacteristics (e.g. angular velocity or acceleration) of a joint (e.g.knee 62) and one or more sensors for sensing activity within one or moremuscles (e.g. knee flexors). Any of the aforementioned sensors could beused to determine the angular characteristic(s) of the joint. Suitablemuscle activity sensors include electromyography (EMG) sensors. Whenmuscle activity-based control is used for the particular energyharvester 60A of FIGS. 6A, 6B, 7 and 8 and energy is harvested frommovement of knee 62 in the extension direction only, feedback signal 122will contain information relating to the angular characteristic(s), suchas position, of knee 62 and muscle activity sensors will be configured(e.g. located) to sense the activity of the knee flexor muscles.

FIG. 11 is a block diagram depicting a method 300 for predicting theexistence of mutualistic conditions using muscle activity-based control.Method 300 is suitable for use with energy harvester 60A of FIGS. 6A,6B, 7 and 8 but may be generalized for use with other embodiments.Method 300 makes use of one or more position sensor(s) which provideinformation relating to the angular position of knee 62 and one or moremuscle activity sensor(s) which provide information relating to theactivity of the knee flexor muscles. Method 300 begins in block 301,where controller 108 reads feedback signal 122 from angular positionsensor(s) 110. Method 300 then proceeds to block 302, where controllerreads feedback signal 122 from muscle activity sensor(s) 110. In block304, controller 108 processes the newly acquired sensor information. Theblock 304 processing may comprise filtering, scaling, offsetting orotherwise digitally manipulating the incoming data, for example. In someembodiments, some of the block 304 processing may occur in the analogdomain (i.e. prior to the block 301 and/or 302 data acquisition). Inthis particular embodiment, block 304 comprises taking a derivative ofthe incoming angular position data to obtain data representative of theangular velocity. In this particular embodiment, block 304 comprisesrectifying and filtering the muscle activity data.

Method 300 then proceeds to block 306 which involves an inquiry as towhether knee 62 is extending. The block 306 inquiry may comprisecomparing the time derivative of the angular position data (i.e. theangular velocity) to zero. If the angular velocity is greater than zero,then knee 62 is extending and if the angular velocity is less than zero,then knee 62 is flexing. Alternatively, the block 306 inquiry mayinvolve looking at historical angular position data to determine if thecurrent angular position is greater than the previous angular position(in which case knee 62 is extending) or if the current angular positionis less than the previous angular position (in which case knee 62 isflexing).

If the block 306 inquiry indicates that knee 62 is flexing (block 306 NOoutput), then method 300 proceeds to block 312, where harvesting isdisabled before looping back to block 301 to collect more data. If onthe other hand the block 306 inquiry indicates that knee 62 is extending(block 306 YES output), then method 300 proceeds to block 308. Block 308involves an inquiry into whether the knee flexor muscles are active.Block 308 may involve and inquiry into whether the activity level of theknee flexor muscles is above a certain threshold (see I_(thresh) in EMGplot 32 of FIG. 2). If the block 308 inquiry indicates that there isinsufficient activity in the knee flexor muscles (block 308 NO output),then method 300 proceeds to block 312, where harvesting is disabledbefore looping back to block 301 to collect more data. If on the otherhand the block 308 inquiry indicates that there is sufficient kneeflexor activity (block 308 YES output), then method 300 proceeds toblock 310.

If method 300 arrives at block 310, then knee 62 is extending (block 306YES output) and the knee flexor muscles are active in trying todecelerate this knee extension (block 308 YES output). Accordingly, theknee flexor muscles are operating in a negative mechanical power modeand conditions are mutualistic. If method 300 arrives at block 310, thencontroller 108 engages harvesting by sending the appropriate controlsignal 120D to switch 136 which in turn couples the movement of knee 62to electrical load 111. In some embodiments, method 300 may optionallyinvolve delaying for a short period before engaging harvesting in block310. The amount of such a delay may be constant or may be separatelyconfigured (or configurable) for each user. The delay may be related tothe period of the walking cycle 21 of a particular host. The delay maybe configured to achieve improved performance (e.g. greater power outputand/or improved user comfort). Method 300 then loops back to block 301to obtain more data.

FIG. 12 is a schematic block diagram of a energy harvesting apparatus60B according to another embodiment of the invention. Energy harvestingapparatus 60B is similar in many respect to energy harvesting apparatus60A and similar reference numerals are used to describe features ofenergy harvester 60B that are similar to corresponding features ofenergy harvester 60A.

Energy harvester 60B differs from energy harvester 60A in that ratherthan having an electronic switch 136 and a roller clutch 130, energyharvester 60B comprises a controllable clutch 150 which mechanicallycouples the movement of knee 62 to, and decouples the movement of knee62 from, electrical load 111. Clutch 150 comprises a mechanical bypass152 which is controlled by signal 120B from controller 108. Whencontroller 108 decides that conditions are mutualistic and energy shouldbe harvested, controller 108 causes control signal 120B to engage clutch150 (i.e. to deactivate mechanical bypass 152) which in turn couples themovement of knee 62 to electrical load 111. When controller 108 decidesthat conditions are non-mutualistic or that energy should not otherwisebe harvested (e.g. because knee 62 is flexing), controller 108 causescontrol signal 120B to disengage clutch 150 (i.e. to activate mechanicalbypass 152) which in turn decouples the movement of knee 62 fromelectrical load 111.

The output of controllable clutch 150 (represented by line 154) is anintermittent and variable amplitude mechanical power. Energy harvester60B also differs from energy harvester 60A in that energy harvester 60Bcomprises a load leveling mechanism 156, which receives intermittent andvariable amplitude mechanical power 154 from clutch 150 and outputsrelatively continuous mechanical power (represented by line 158).Relatively continuous mechanical power 158 is delivered to gearing 134which outputs corresponding mechanical power 114 which may have adifferent speed and torque that mechanical power 158. Load levelingmechanism 156 is not necessary. However, load leveling mechanism 156 mayimprove the performance of energy harvesting apparatus 60B becausegenerator 104 may exhibit better performance (i.e. better powerconversion efficiency) when input mechanical power 114 is continuousrather than intermittent and variable.

In other respects, energy harvester 60B is similar to energy harvester60A.

One advantage of energy harvester 60B over energy harvester 60A is thatclutch 150 mechanically disengages gearing 134 and generator 104 fromknee 62. Thus, when clutch 150 is disengaged and energy harvester 60B isnot harvesting energy, the host does not have to move gearing 134 orgenerator 104. In contrast, energy harvester 60A requires that the hostmove gearing 134 and generator 104 when knee 62 is extending (i.e.roller clutch 130 is engaged) even if switch 136 is open and energy isnot being harvested. When knee 62 is flexing, roller clutch 130 ofenergy harvester 60A provides benefits similar to those of clutch 150 ofenergy harvester 60B by mechanically disengaging gearing 134 andgenerator 104 from knee 62.

Energy harvesters 60A, 60B described above only harvest energyassociated with the extension of knee 62. Those skilled in the art willappreciate that energy harvesters 60A, 60B could be modified to onlyharvest energy associated with the flexion of knee 62 when the energyharvesting conditions are primarily mutualistic. Such energy extractionconditions are exhibited, for example, in region 28A of plot 28.

Energy harvester 60A could be modified to harvest the energy associatedwith knee flexion by reconfiguring roller clutch 130 to engage gearing134 when knee 62 is flexing and to disengage gearing 134 when knee 62 isextending (see FIG. 8). Energy harvester 60B does not require hardwaremodification to harvest energy during knee extension. Method 200 may bemodified to harvest energy during knee flexion and when the energyharvesting conditions are primarily mutualistic by modifying block 206and/or block 208 appropriately. By way of non-limiting example, theblock 206 inquiry could be modified to consider whether stance phase 21Ahad just begun. It would not be necessary to change the block 208inquiry. Such modification would allow controller 108 to use method 200to engage energy harvesting during the time corresponding to region 28Aand to disengage energy harvesting otherwise. Method 300 may be modifiedto harvest energy during knee flexion and when the energy harvestingconditions are primarily mutualistic by modifying the block 306 inquiryto consider whether knee 62 is flexing and by modifying the block 308inquiry to consider whether the knee extensor muscles are active. Suchmodification would allow controller 108 to use method 300 to engageenergy harvesting during the time corresponding to region 28A and todisengage energy harvesting otherwise.

In some embodiments, energy may be harvested both when knee 62 isextending and when knee 62 is flexing. Energy harvesters which canharvest energy during extension and flexion may be said to bebi-directional. FIGS. 13A, 13B and 14 show a bi-directional energyharvesting apparatus 60C according to another embodiment of theinvention. Energy harvester 60C is configured to harvest energy duringknee flexion and during knee extension and primarily when the energyharvesting conditions are mutualistic. Energy harvesting apparatus 60Cis similar in many respects to energy harvesting apparatus 60A andsimilar reference numerals are used to describe features of energyharvester 60C that are similar to corresponding features of energyharvester 60A.

Energy harvester 60C differs from energy harvester 60A in that energyharvester 60C comprises a mechanical rectifier 164 which converts bothdirections of motion of knee joint 62 (i.e. flexion and extension) intoa single direction mechanical power signal. Mechanical rectifier 164 maycomprise a pair of uni-directional torque transfer mechanisms 130, 160configured in opposing directions with one of the torque transfermechanisms coupled to a mechanical direction inverter 166. In theillustrated embodiment, torque transfer mechanisms 130, 160 compriseroller clutches 130, 160. Roller clutches 130, 160 are configured suchthat: (i) roller clutch 130 directly engages gearing 134 (as representedby line 142A) when knee 62 moves in the extension direction anddisengages from gearing 134 (via mechanical bypass 132) when knee 62moves in the flexion direction; and (ii) roller clutch 160 engagesgearing 134 via direction inverter 166 (as represented by line 142B)when knee 62 moves in the flexion direction and disengages from gearing134 (via mechanical bypass 162) when knee 62 moves in the extensiondirection. Because of direction inverter 166 (which acts when knee 162is moving in the flexion direction and roller clutch 160 is engaged),movement of knee 162 in both the flexion direction and the extensiondirection cause movement of gearing 134 in the same direction. Directioninverter 166 may be implemented by coupling an additional gear betweenroller clutch 160 and gearing 134, for example. Those skilled in the artwill appreciate that there are a variety of additional or alternativemechanisms that could be used to implement direction inverter 166.

In other respects, the components of energy harvester 60C are similarcomponents of energy harvester 60A.

In contrast to energy harvester 60A, controller 108 may be configured tocause signal 120D to close switch 136 (i.e. coupling the motion of knee62 to load 111) when: (i) knee 62 is extending and the energy harvestingconditions are determined by controller 108 to be primarily mutualistic;and/or (ii) knee 62 is flexing and the energy harvesting conditions aredetermined by controller 108 to be primarily mutualistic. Referring toFIG. 2, region 28B (of plot 28) exhibits mutualistic conditions in swingphase 21B, where knee 62 is extending and the knee flexor muscles areactive to decelerate this extension, and region 28A exhibits mutualisticconditions in stance phase 21A, where knee 62 is flexing and the kneeextensor muscles are active to decelerate this flexion.

Plot 28 (FIG. 2) also shows that there is a small region 28C exhibitingnon-mutualistic conditions between mutualistic region 28B and anadjacent mutualistic region 28A. In theory, energy could be harvested inregion 28B and region 28A only. However, in practice, for harvestingenergy from a walking human, the inventors have determined that it issometimes convenient to harvest energy from the onset of mutualisticregion 28B, through mutualistic region 28B, non-mutualistic region 28Cand subsequent mutualistic region 28A and to discontinue energyharvesting at the conclusion of mutualistic region 28A. Energyharvesting in region 28C is non-mutualistic. However, thisnon-mutualistic energy harvesting in region 28C is relativelyinsignificant in terms of its additional metabolic cost when compared tothe metabolic power savings associated with mutualistic energyharvesting in regions 28A and 28B. In addition, energy harvesting inregions 28A, 28B and 28C reduces the frequency of engagement anddisengagement of load 111 (which would occur if energy was harvested inregions 28A and 28B only) and avoids the possible negative impact ofsuch rapid engagement and disengagement on the coordination of the host.

As with the extension only energy harvester 60A, controller 108 ofenergy harvester 60C may make the decision as to when to harvest energyusing model-based control techniques or muscle activity-based controltechniques so as to harvest energy under mutualistic conditions and todisengage energy harvesting during non-mutualistic conditions.

FIG. 15 is a block diagram illustrating a method 400 for predicting theexistence of primarily mutualistic conditions. Method 400 is suitablefor use with energy harvester 60C of FIGS. 13A, 13B and 14. Thoseskilled in the art will appreciate, however, that method 400 may bemodified for use with other embodiments. FIG. 16 shows a number of plotsrelating to the harvesting of energy while the host is walking usingenergy harvester 60C in accordance with method 400. Characteristics ofthe FIG. 16 plots (e.g. the amplitude and frequency) may vary for eachindividual host and for the conditions being experienced by a particularhost.

Plot 420 shows the angle of knee joint 62 of a particular host during awalking motion. As discussed above, controller 108 may determine theangle of knee joint 62 using feedback signal 122 from sensor(s) 110(i.e. potentiometer 113 in the illustrated embodiment). When the host iswalking, each cycle 21 of plot 402 comprises a stance phase 21A and aswing phase 21B. Plot 423 shows the angular velocity of knee joint 62.The angular velocity plot 423 may be obtained by taking the derivativeof the angular position plot 420, for example. Plot 422 representscontrol signal 120D which, in the illustrated embodiment, is a binarysignal having an enable harvest level and a disable harvest level. Whenplot 422 is at its enable harvest level, controller 108 outputs a signal120D which causes switch 136 to close. When switch 136 is closed, themotion of knee 62 is coupled to electrical load 111, such thatelectrical power output signal 118 is delivered to load 111. When plot422 is at its disable harvest level, controller 108 outputs a signal120D which causes switch 136 to open, thereby decoupling the motion ofknee 62 from electrical load 111 and disengaging energy harvesting.

Method 400 makes use of model-based control. In the illustratedembodiment, method 400 also makes use of sensor(s) which provideinformation relating to the angular position (or other angularcharacteristic(s)) of knee 62. In alternative embodiments, method 400may make use of other sensors that detect one or more characteristicsassociated with a repetitive motion (e.g. walking). In many respects,model-based control method 400 is similar to model-based control method200 (FIG. 9). Blocks 402, 404 and 406 are substantially similar toblocks 202, 204 and 206 of model-based control method 200 (FIG. 9) andrespectively involve reading feedback signal 122 from angular positionsensors 110; processing the newly acquired sensor information; andconducting an inquiry into whether the processed sensor data indicatesthat knee 62 has just begun the swing phase knee extension.

If the block 406 inquiry indicates that the swing phase knee extensionhas just begun (block 406 YES output), then method 400 proceeds to block410 (which imposes a short delay). Block 410 may be similar to block 210of method 200. From block 410, method 400 proceeds to block 412, wherecontroller 108 commences energy harvesting in a manner similar to block212 of method 200. Method 400 then loops back to block 402, wherecontroller 108 obtains more angular position data from sensors 110.

The next time method 400 arrives at block 406, the swing phase kneeextension will have begun on the previous loop, so method 400 will exitblock 406 through the block 406 NO output into block 408. In general,block 408 involves determining whether the energy harvesting engaged inblock 212 should be discontinued (e.g. because conditions are no longermutualistic). Block 408 may be substantially similar to block 208 ofmethod 200.

If the block 408 inquiry indicates that the stance phase knee extensionhas not just begun (block 408 NO output) and switch 136 is closed (i.e.energy harvester 60C is harvesting energy), then switch 136 remainsclosed and energy harvester 60C continues to harvest energy while method400 loops back to block 402. If on the other hand, the block 408 inquiryindicates that stance phase knee extension has just begun (block 408 YESoutput) and switch 136 is closed (i.e. energy harvester 60C isharvesting energy), then method 400 proceeds to delay block 414. Delayblock 414 may be similar to delay block 214 of method 200. Method 400then proceeds to block 416, where controller 108 disengages energyharvesting in a manner similar to block 216 of method 200. After block416, method 400 again loops back to block 402. If the block 408 inquiryindicates that stance phase knee extension has not just begun (block 408NO output) and switch 136 is open (i.e. energy harvester 60C is notharvesting energy), then method 400 loops back to block 402 withoutchanging the status of switch 136.

Like the model-based control methods for harvesting energy duringwalking shown in FIGS. 9 and 10, model-based control similar to that ofFIGS. 15 and 16 may be used for other cyclical movements.

FIG. 17 is a block diagram illustrating a method 500 for predicting theexistence of primarily mutualistic conditions suitable for use withenergy harvester 60C of FIGS. 13A, 13B and 14 using muscleactivity-based control. Method 500 makes use of one or more positionsensor(s) which provide information relating to the angular position (orother angular characteristic(s)) of knee 62 and a plurality of muscleactivity sensor(s) which provide information relating to the activity ofthe knee flexor muscles and to the activity of the knee extensormuscles. Blocks 501, 502 and 503 of method 500 are similar to blocks301, 302 and 303 of method 300 and respectively involve obtainingfeedback signal 122 from angular position sensor(s) 110, obtainingfeedback signal 122 from muscle activity sensor(s) 110; and processingthe newly acquired sensor information.

Block 506 involves an inquiry into whether the knee flexor muscles areactive. Block 506 may be performed in a manner similar to block 308 ofmethod 300. If the block 506 inquiry indicates that there is aninsufficient level of activity in the knee flexor muscles (block 506 NOoutput), then method 500 proceeds to block 520. On the other hand, ifthe block 506 inquiry indicates that the knee flexor activity issignificant (block 506 YES output), then method 500 proceeds to block508.

Block 508 involves an inquiry into whether or not knee 62 is extending.The block 508 inquiry may be performed in a manner similar to block 306of method 300. If the block 508 inquiry indicates that knee 62 is notextending (block 508 NO output), then method 500 loops back to block 501to collect more data. If on the other hand the block 508 inquiryindicates that knee 62 is extending (block 508 YES output), then method500 proceeds to block 510, where controller 108 engages harvestingbefore looping back to block 501 to collect more data. In someembodiments, method 500 may optionally involve delaying for a shortperiod before engaging harvesting in block 510. The amount of such adelay may be constant or may be separately configured (or configurable)for each user. The delay may be related to the period of the walkingcycle 21 of a particular host. The delay may be configured to achieveimproved performance (e.g. greater power output and/or improved usercomfort). Method 500 then loops back to block 501 to obtain more data.

Block 520 involves an inquiry into whether the knee extensor muscles areactive. Block 520 may be performed in a manner similar to block 308 ofmethod 300 except that block 520 involves extensor muscles rather thanflexor muscles. If the block 520 inquiry indicates that there is aninsufficient level of activity in the knee extensor muscles (block 520NO output), then method 500 loops back to block 501 to collect moredata. On the other hand, if the block 520 inquiry indicates that theknee extensor activity is significant (block 520 YES output), thenmethod 500 proceeds to block 514.

Block 514 involves an inquiry into whether or not knee 62 is flexing.The block 514 inquiry may comprise comparing the time derivative of theangular position data (i.e. the angular velocity) to zero. If theangular velocity is less than zero, then knee 62 is flexing.Alternatively, the block 306 inquiry may involve looking at historicalangular position data to determine if the current angular position isless than the previous angular position (in which case knee 62 isflexing). If the block 514 inquiry indicates that knee 62 is not flexing(block 514 NO output), then method 500 proceeds to block 518 wherecontroller 108 disengages harvesting (if harvesting was engaged) beforelooping back to block 501 to collect more data. If on the other hand theblock 514 inquiry indicates that knee 62 is flexing (block 514 YESoutput), then method 500 proceeds to block 516 where controller 108engages harvesting before looping back to block 501 to collect moredata.

It can be see from FIG. 17, that energy harvesting is engaged (in block510) when knee 62 is extending (block 508 YES output) and the kneeflexor muscles are active to decelerate this extension (block 506 YESoutput). These conditions correspond to mutualistic region 28B. FIG. 17also shows that energy harvesting is engaged (in block 516) when knee 62is flexing (block 514 YES output) and the knee extensor muscles areactive to decelerate this flexion (block 520 YES output). Theseconditions correspond to mutualistic region 28A.

Method 500 is configured to engage energy harvesting through regions28A, 28B and 28C (FIG. 2). After engaging harvesting, method 500 doesnot disengage harvesting until block 518. Block 518 corresponds to thebeginning of the stance phase knee extension (i.e. the beginning ofregion 22B of plot 22 (FIG. 2) and the end of region 28A of plot 28(FIG. 2).

In some embodiments, controller 108 can be configured to allownon-mutualistic harvesting. For example, controller 108 can beconfigured to output the appropriate signal 120A, 120B, 120C, 120D tomaintain the engagement between the movement of knee 62 and theelectrical load 111. In some embodiments, the control system forselectively engaging and disengaging energy harvesting is removed fromany of the above-described embodiments, such that they harvest energyunder mutualistic conditions and non-mutualistic conditions. By way ofnon-limiting example, energy harvesting apparatus 60A (FIG. 8) may beconfigured to harvest energy under mutualistic and non-mutualisticconditions by configuring controller 108 in a suitable manner or byremoving controller 108, switch 136 and/or sensors 110. When modified inthis manner, energy harvester 60A still only harvest energy when knee 62is extending, because of roller clutch 130 (i.e. energy harvester isuni-directional).

While modification of any of the above-described embodiments (orconfiguring their controllers) to harvest energy under non-mutualisticconditions can still produce a reasonable amount of energy, such energyproduction will come at the expense of increased effort from the host,as the host will have to exert extra mechanical power to move generator104 under non-mutualistic conditions. FIG. 18 shows a number of plotsrelating to the harvesting of energy while the host is walking usingenergy harvester 60A configured to harvest energy under mutualistic andnon-mutualistic conditions. Characteristics of the FIG. 18 plots (e.g.amplitude and frequency) may vary for each individual host and forspecific conditions being experienced by a particular host. Plot 602represents the position of knee 62 (as measured by sensors 110), plot600 represents the instantaneous output power of signal 118 and plot 604represents the average output power of signal 118.

FIG. 18 shows that during a typical walking cycle 21 energy harvestingoccurs during both periods when knee 62 is extending (i.e. when theslope of plot 602 is positive). Plot 604 indicates that when harvestingunder mutualistic and non-mutualistic conditions, the average outputpower generated at load 111 by energy harvester 60A is 3.2 W which isgreater than the 2.4 W output when harvesting under primarilymutualistic conditions (FIG. 10). However, harvesting energy undernon-mutualistic conditions requires significant energy input from thehost.

FIGS. 21A, 21B and 21C respectively depict EMG plots showing muscleactivity levels and electrical power generation for a human walking.FIG. 21A depicts EMG plots 30 for knee extensor muscles and 32 for kneeflexor muscles and electrical power plot 902 for a human walking with noenergy harvesting. FIG. 21B depicts EMG plots 904 for knee extensormuscles and 906 for knee flexor muscles and electrical power plot 908for a human walking with mutualistic energy harvesting associated withknee extension only. FIG. 21C depicts EMG plots 910 for knee extensormuscles and 912 for knee flexor muscles and electrical power plot 914for a human walking with both mutualistic and non-mutualistic energyharvesting associated with knee extension only (i.e. when the motion ofthe knee in the extension direction is always coupled to the electricalload).

It can be seen (by comparing plot 906 of FIG. 21B with plot 32 of FIG.21A) that mutualistic energy harvesting during knee extension reducesthe knee flexor activity associated with decelerating the kneeextension. Plot 908 shows that electrical energy is generated duringmutualistic energy harvesting. It can also be seen (by comparing plot910 of FIG. 21C with plot 904 of FIG. 21B) that non-mutualistic energyharvesting during knee extension increases knee extensor activityassociated with moving the knee during the stance phase knee extension.Comparing plot 914 and plot 908 shows that more electrical energy isgenerated when harvesting energy during mutualistic and non-mutualisticconditions (relative to mutualistic conditions only), but that thisexcess electrical energy harvesting comes at the expense of extra effortfrom the knee extensor muscles.

FIG. 22 shows a plot of heart rate versus time for a human walking withno energy harvesting (region 916), with mutualistic energy harvestingassociated with knee extension only (region 918) and with bothmutualistic and non-mutualistic energy harvesting associated with kneeextension only (region 920). Heart rate is a general indicator of thephysical effort involved with an associated activity. Comparing region916 and region 918 of FIG. 22 shows that less effort is required to walkwhen harvesting energy under mutualistic conditions (region 918) than isrequired to walk without harvesting energy (region 916). Comparingregion 920 to regions 916 and 918 of FIG. 22 shows that more effort isrequired to walk when harvesting energy under mutualistic andnon-mutualistic conditions (region 920) than is required to walk withoutharvesting energy (region 916) or than is required to walk whileharvesting energy under mutualistic conditions (region 918).

As shown in FIG. 4B, energy harvesting apparatus 70 may be provided aspart of, or as an addition to, an orthopedic prosthesis 74. In theillustrated embodiment, energy harvester 70 harvests energy across ajoint 72 (or joints) between segments 74A, 74B of prosthesis 74 in orderto harvest mechanical energy transmitted by joint 72 in much the samemanner that any of the above-described energy harvesting apparatus.Energy harvester 70 may incorporate components that are similar to thoseof the above-described energy harvesting apparatus. Energy harvester 70may be integrated with prosthesis 74. Preferably, energy harvester 70harvests energy under primarily mutualistic conditions. Energy harvester70 may be provided with a control mechanism that permits a user toengage or disengage energy harvesting and/or to change an operationalmode of energy harvester 70.

In the illustrated embodiment, energy harvester 70 is used in connectionwith a prosthesis wherein joint 72 is a knee joint (FIG. 4). Knee jointsof prosthetic limbs are typically braked (i.e. decelerated) by passivedevices, such as hydraulics (e.g. Ossur™ Total Knee), or by activedevices, such as a Magnetorheologic (MR) Fluid Actuator (e.g. Ossur™Rheo Knee). Energy harvester 70 uses a generator similar to generator104 to perform negative work on joint 72, thereby decelerating themotion of joint 72. The generator converts this mechanical energy intoelectrical energy which may be used, in whole or in part, to powerelectrical components (not shown) of prosthesis 74. Harvesting energy inthis manner can greatly increase the efficiency of prosthesis 74,allowing for smaller, lighter batteries and longer periods betweencharges.

Energy harvester 70 may comprise a controller similar to controller 108which may selectively engage motion of joint 72 to an electrical loadunder mutualistic conditions. Energy harvester 70 may comprise one ormore sensors (similar to sensors 110) to detect the angular position ofjoint 72. Such sensors may also detect information in respect of anactuator (not shown) acting at joint 72. For example, such sensors maydetect information, such as current draw for a MR Fluid Actuator orforce and velocity signals from a hydraulic actuator, and the controllermay use this information to make decisions as to when conditions aremutualistic.

In some embodiments, energy harvester 70 is used in the place of theconventional actuator for joint 72 of prosthesis 74. Energy harvester 70may be selectively engaged and disengaged at the correct part of thewalking step cycle based on feedback signals related to joint angularvelocities, ground reaction force under the prosthetic leg, andinformation from the intact leg, for example. Exemplarily control logicfor an embedded energy harvester is illustrated in FIG. 12.

FIG. 19 schematically depicts a method 700 for controlling energyharvester 70 so that it will harvest energy during primarily mutualisticconditions. Method 700 involves reading available sensor data in block702 and processing the sensor data in block 704. Blocks 706, 708, 714and 720 involve using the processed sensor data to make determinationsabout the direction of motion of joint 72 and the net torque on joint72. FIG. 19 shows that the energy is harvested (block 710) when joint 72is moving in an flexion direction (block 706 YES output) and the nettorque on joint 72 is in an extension direction (block 708 YES output).Similarly, energy is harvested (block 716) when joint 72 is moving in anextension direction (block 720 YES output) and the net torque on joint72 is in a flexion direction (block 714 YES output).

FIG. 4C depicts an energy harvesting apparatus 80 according to anotherembodiment of the invention wherein energy harvesting apparatus 80 isimplanted within the body of the host. In the illustrated embodiment,energy harvester 80 is placed across the anterior aspect of the anklejoint 82 with an anatomical location similar to that of the tibialisanterior muscle 84. In other embodiments, energy harvester 80 could beconfigured to work in conjunction with another joint (or joints) betweencorresponding body segments. Energy harvester 80 may be configured toharvest energy in a mutualistic mode and to thereby assist a specificmuscle (or group of muscles) during the phases in which the muscle(s)operate in negative mechanical power modes. In some embodiments, energyharvester 80 may be configured to also harvest energy duringnon-mutualistic modes or to cease energy harvesting altogether.Switching between operational modes may be accomplished by the user, asdesired, using a remote switch (not shown), for example.

In general, the components and operation of implanted energy harvester80 may be similar to those of energy harvesters 60, 60A, 60B, 60C and 70described above. In some embodiments, the generator (not shown) ofenergy harvester 80 comprises a piezoelectric generator to convertmechanical displacement in to electrical energy. In such embodiments,load leveling and gearing may not be required. In the illustratedembodiment, one end of the generator is attached to the shin bone andthe other end to a foot bone. This may be done, for example, using bonescrews made of suitable bio-compatible material(s), such as tantalum—arelatively strong material that is not rejected by the body. Some of thecomponents of energy harvester 80 (e.g. the controller and powerconditioning circuitry) may be housed in a small implanted hermeticcontainer (not shown). The container may be made, for example, oftitanium or some other suitable bio-compatible material.

To operate in a mutualistic mode, the controller of energy harvester 80uses information from suitable sensors to determine when the muscle itis aiding is operating in a negative mechanical power mode. As discussedabove, a muscle operates in a negative mechanical power mode when themuscle is lengthening and the muscle is active (i.e trying to contract).The velocity of the muscle can be sensed, for example, usingaccelerometers implanted in the muscle and the activity of the musclecan be sensed, for example, using EMG electrodes implanted in themuscle. Signals from these sensors may be conducted back to theimplanted controller by way of suitable conductors such asTeflon™-coated wires.

The controller of energy harvester 80 may be configured to engageharvesting when the associated muscle is active and the muscle islengthening. FIG. 20 is a schematic block diagram showing a method fordetermining when to selectively cause energy harvesting apparatus 80 toharvest energy according to a particular embodiment of the invention.Method 800 senses data (block 802) and processes the incoming data(block 804). Method 800 engages harvesting (block 810) when the muscleis active (block 806 YES output) and when the associated muscle islengthening (block 808 YES output). Otherwise harvesting is disengaged(block 812).

In the illustrated embodiment, the controller of energy harvester 80 maybe configured to harvest energy when tibialis anterior muscle 84 isactive and tibialis anterior muscle 84 is lengthening. The resultingelectrical energy produced by harvester 80 may be used to charge abattery and/or used directly to power another implanted device. Forexample, the electrical power may be used to charge a small storagebattery, such as a lithium-iodine battery, that may be contained withinthe box that contains the controller.

During walking, energy harvester 80 operates as follows. When the leg isin middle of its swing phase, the electrical load is disengaged frommovement about the ankle. Just prior to heel-strike, the tibialisanterior muscle is activated which is sensed using one or more muscleactivity sensors. This activity in the tibialis anterior muscle meetsone condition for engaging energy harvesting. At heel-strike, thetibialis anterior muscle is lengthened which is sensed using one or moreaccelerometers or other suitable sensor(s). This lengthening of thetibialis anterior muscle meets the second condition for energyharvesting. The controller then couples the electrical load to themovement of ankle 82. As the stance phase progresses, the sensors detectthat the tibialis anterior muscle stops lengthening, causing thecontroller to disengage energy harvesting.

While a number of exemplary aspects and embodiments have been discussedabove, those of skill in the art will recognize certain modifications,permutations, additions and sub-combinations thereof. For example:

-   -   Some of the embodiments described above involve selectively        harvesting energy in a mutualistic mode using the muscles        associated with the knee of a human. Those skilled in the art        will appreciate that selectively harvesting energy in a        mutualistic mode from the muscle(s) associated with other joints        is considered to be within the scope of the invention. By way of        non-limiting example, one may design similar systems to harvest        energy from the muscles associated with movement of an ankle,        shoulder, elbow, finger, wrist, neck, hip or the like. Also,        energy harvesters according to other embodiments are configured        to extract energy from a plurality of joints.    -   Some of the embodiments described above involve selective energy        harvesting in a mutualistic mode during particular movements,        such as walking. In other embodiments, selective energy        harvesting in a mutualistic mode may be provided for other types        of movements. By way of non-limiting example, such movements may        involve knee bends, descending stairs or sloped surfaces,        cycling, dancing, typing, throwing or the like.    -   In addition to operating in a mutualistic mode, any of the        above-discussed embodiments may be configured to operate in a        non-mutualistic mode, where electrical energy is harvested at        the expense of additional effort required by the host. A benefit        of non-mutualistic mode energy harvesting is that there may be        more power available for harvesting when compared to mutualistic        mode energy harvesting alone.    -   The electrical energy generated by any of the above-discussed        embodiments may be used in any suitable manner. For example,        this electrical energy may be used directly to power electrical        devices or this electrical energy may be stored for later use.        Non-limiting examples of electrical devices which may be powered        by the electrical energy generated by the above-discussed        embodiments include orthopedic or neural prosthetic devices, and        portable electronic devices (e.g. cellular telephones, personal        digital assistants, global positioning system receivers, laptop        computers or the like).    -   Some of the embodiments described above make use of a roller        clutch as a uni-directional torque transfer mechanism. In        alternative embodiments, other suitably configured,        uni-directional torque transfer mechanisms, such as a ratchet        mechanism or the like, may be used in place of a roller clutch.    -   Bi-directional energy harvesting apparatus (e.g. energy        harvester 60C of FIGS. 13A, 13B and 14) may be configured to        have different gear ratios for flexion and extension. Such        different gear ratios may compensate for circumstances where the        mechanical power input tends to have different torques and/or        different velocities in either direction.    -   It is not necessary that bi-directional energy harvesting        apparatus incorporate a mechanical rectifier. Rectification may        be performed in the electrical domain. For example,        uni-directional energy harvester 60A may be made bi-directional        by simply removing roller clutch 130 and modifying rectifier 138        to accommodate bidirectional electrical output from generator        104.    -   Bi-directional energy harvesting apparatus 60C (FIG. 14) is        described as having a electronic switch 136 for coupling the        body 61 of the host to electrical load 111 and for decoupling        the body 61 of the host from electrical load 111. In other        embodiments, energy harvester 60C comprises a controllable        mechanical clutch or the like (similar to clutch 150 if energy        harvester 60B (FIG. 12) for coupling the body 61 of the host to        electrical load 111 and for decoupling the body 61 of the host        from electrical load 111. Such a controllable clutch could be        located between mechanical connection 100 and mechanical        rectifier 164 or between mechanical rectifier 164 and gearing        134, for example. Controller 108 may control such a controllable        clutch using a corresponding signal 120B.    -   Some embodiments may comprise different generator types or        different generator components. For example, it may be        beneficial to use an electro-active polymer or piezo-electric        generator. In some embodiments, the generator may generate        electricity in response to linear motions of generator        components relative to one another. It may also be beneficial to        use two or more generators.    -   Some embodiments may comprise different transmission        configurations or different transmission components. Gearing may        be driven directly (rather than using roller clutches).        Mechanisms other than traditional gears may be used to change        the torque and speed characteristics of the input mechanical        power. Examples of such mechanisms include a capstan drive or        lever arm. Other load leveling mechanisms may be used, such as a        flywheel, for example. In some embodiments, load levelling        and/or gearing are not required. In other embodiments, the        gearing serves to decrease the velocity of the input mechanical        power, which may be desirable when using certain generators such        as piezoelectric generators, for example.    -   Energy harvesting apparatus 60, 60A, 60C may be modified to add        load leveling mechanisms similar to load leveling mechanism 156        of energy harvesting apparatus 60B. For example, energy        harvester 60A (FIG. 8_ could be modified to provide a load        leveling device at line 142 (i.e. between roller clutch 130 and        gearing 134, for example. Such load leveling devices could be        used to deliver relatively continuous mechanical power to their        corresponding gearing 134 and generators 104.    -   Method 400 (FIG. 15) and method 500 (FIG. 17) describe        techniques for harvesting energy associated with knee extension        and with knee flexion. Both of these methods involve harvesting        energy in the small non-mutualistic region 28C of plot 28 (see        FIG. 2). Either of these methods could be modified to harvest        energy only in exclusively mutualistic regions (e.g. regions        28A, 28B of plot 28). For example, method 500 could be modified        to harvest energy exclusively in mutualistic regions by        providing a disengage harvesting block (similar to block 518) on        the NO output of blocks 508 and 520.    -   Delays similar to blocks 210 and 214 of method 200 may be        incorporated into other embodiments. By way of non-limiting        example, a similar delay could be inserted between blocks 308        and 310 of method 300 (FIG. 11) and/or between blocks 308 and        312 of method 300 and/or between blocks 306 and 312 of method        300. Delays could similarly be inserted into methods 500 (FIG.        17), 700 (FIG. 19), 800 (FIG. 20) and any other embodiment.    -   Thresholds used to assess whether conditions are mutualistic or        non-mutualistic (e.g. φ_(thresh) and I_(thresh)) may be constant        or variable and may also be user configurable. Such thresholds        may be related to the slope of the terrain. Such thresholds may        be adaptive. By way of non-limiting example, if the slope of the        terrain changes or the period of a repetitive motion changes,        then the threshold may change accordingly.    -   In some embodiments, the electrical coupling between generator        104 and load 118 may comprise a wireless coupling. For example,        electrical power signal 116 or 118 could be transmitted by way        of an RF transmitter to a load 111 equipped with a suitable RF        receiver.    -   The above described embodiments comprise a controller 108. In        other embodiments, a other control circuits may be used to        provide the functionality of controller 108. Such other control        circuits may comprise analog electronic circuitry and/or digital        electronic circuitry and may comprises a controller of the type        described above. The invention should be understood to include        any control circuit capable of performing the functions of        controller 108 described above.    -   An energy harvesting device according to the invention may be        built into a garment or made to be worn under or over a garment.    -   The embodiments described above relate to harvesting energy from        humans, but those skilled in the art will appreciate that energy        could be harvested from animals (e.g. livestock) in accordance        with the above-described methods and apparatus.

Accordingly, the scope of the invention should be construed inaccordance with the substance defined by the following claims.

The terms and expressions which have been employed in the foregoingspecification are used therein as terms of description and not oflimitation, and there is no intention, in the use of such terms andexpressions, of excluding equivalents of the features shown anddescribed or portions thereof, it being recognized that the scope of theinvention is defined and limited only by the claims which follow.

1. An apparatus for harvesting energy from motion of one or more humanor other animal joints, the apparatus comprising: a generator coupled toone or more human or animal joints for converting mechanical energyassociated with motion of the one or more joints into correspondingelectrical energy; one or more sensors for sensing one or morecorresponding characteristics associated with motion of a body of thehuman or animal; and a controller connected to receive the one or moresensed characteristics and configured to modify at least one of: a firstcoupling of mechanical energy associated with the motion of the one ormore joints to the generator; and a second coupling of electrical energyfrom the generator to a load; based at least in part on the one or moresensed characteristics.
 2. An apparatus according to claim 1 wherein thecontroller is configured to modify at least one of the first and secondcouplings by selectively: engaging energy harvesting by completing atleast one of the first and second couplings; and disengaging energyharvesting by decoupling at least one of the first and second couplings.3. An apparatus according to claim 2 wherein the controller isconfigured to assess whether the motion of the one or more joints isassociated with mutualistic conditions or non-mutualistic conditionsbased at least in part on the one or more sensed characteristics and toselectively engage energy harvesting when motion of the one or morejoints is associated with particular mutualistic conditions and toselectively disengage energy harvesting when motion of the one or morejoints is associated with non-mutualistic conditions.
 4. An apparatusaccording to claim 3 wherein at least one of the one or more sensedcharacteristics is related to an angular characteristic of the one ormore joints.
 5. An apparatus according to claim 3 wherein the motion ofthe one or more joints is associated with mutualistic conditions whenone or more muscles associated with the one or more joints are acting todecelerate motion of the one or more joints.
 6. An apparatus accordingto claim 3 wherein the motion of the one or more joints is associatedwith mutualistic conditions when one or more muscles associated with theone or more joints are producing torque in a particular direction andthe motion of the one or more joints is in the opposing direction.
 7. Anapparatus according to claim 3 wherein the motion of the one or morejoints is associated with mutualistic conditions when one or moremuscles associated with the one or more joints are lengthening and thesame one or more muscles have an activity level above an activity levelthreshold.
 8. An apparatus according to claim 3 wherein the motion ofthe one or more joints is associated with mutualistic conditions whencompleting the coupling of mechanical energy associated with the motionof the one or more joints to the generator and electrical output of thegenerator to the load causes at least one of: decreased muscle activityassociated with one or more muscles that cross the one or more joints;decreased effort associated with the motion of the one or more joints;decreased metabolic cost associated with the motion of the one or morejoints; and decreased heart rate associated with the motion of the oneor more joints.
 9. An apparatus according to claim 3 wherein the firstcoupling comprises a mechanism which, when engaged, transfers themechanical energy associated with the motion of the one or more jointsto the generator and, when disengaged, decouples the transfer of themechanical energy associated with the motion of the one or more jointsfrom the generator.
 10. An apparatus according to claim 9 wherein themechanism is engaged during motion of the one or more joints in a firstdirection and is disengaged during motion of the one or more joints in asecond direction opposite the first direction.
 11. An apparatusaccording to claim 10 wherein the mechanism comprises a roller clutch.12. An apparatus according to claim 9 wherein the mechanism isswitchable between its engaged configuration and its disengagedconfiguration in response to a signal from the controller.
 13. Anapparatus according to claim 3 wherein the first coupling comprises auni-directional torque transfer mechanism for transferring mechanicalenergy associated with the motion of the one or more joints in a firstdirection to the generator and for decoupling the transfer of mechanicalenergy associated with the motion of the one or more joints in a seconddirection opposite the first direction from the generator.
 14. Anapparatus according to claim 3 wherein the first coupling comprises amechanical rectifier connected such that motion of the one or morejoints in a first direction causes corresponding motion of a mechanicalrectifier output component in a corresponding first direction and motionof the one or more joints in a second direction opposed to the firstdirection causes corresponding motion of the mechanical rectifier outputcomponent in the corresponding first direction.
 15. An apparatusaccording to claim 14 wherein the mechanical rectifier comprises: a pairof uni-directional torque transfer mechanisms connected such that motionof the one or more joints in the first direction causes correspondingmotion of a first one of the pair of uni-directional torque transfermechanisms in the corresponding first direction and motion of the one ormore joints in the second direction causes corresponding motion of asecond one of the pair of uni-directional torque transfer mechanisms ina corresponding second direction opposed to the corresponding firstdirection; and a mechanical inverter coupled to the second one of thepair of uni-directional torque transfer mechanisms for converting motionof the second one of the pair of uni-directional torque transfermechanisms in the corresponding second direction to motion of theinverter in the corresponding first direction.
 16. An apparatusaccording to claim 3 wherein the second coupling comprises a switchwhich, when closed, transfers electrical energy output from thegenerator to the load and, when open, decouples the transfer ofelectrical energy output from the generator to the load.
 17. Anapparatus according to claim 16 wherein the switch is switchable betweenits open configuration and its closed configuration in response to asignal from the controller, wherein, if the controller determines thatthe motion of the one or more joints is associated with the particularmutualistic conditions, the controller is configured to engage energyharvesting by switching the switch to its closed configuration andwherein, if the controller determines that the motion of the one or morejoints is associated with non-mutualistic conditions, the controller isconfigured to disengage energy harvesting by switching the switch to itsopen configuration.
 18. An apparatus according to claim 16 wherein thefirst coupling comprises a mechanism which, when engaged, transfers themechanical energy associated with the motion of the one or more jointsto the generator and, when disengaged, decouples the transfer of themechanical energy associated with the motion of the one or more jointsfrom the generator.
 19. An apparatus according to claim 18 wherein themechanism is engaged during motion of the one or more joints in a firstdirection and is disengaged during motion of the one or more joints in asecond direction opposite the first direction.
 20. An apparatusaccording to claim 19 wherein the mechanism comprises a roller clutch.21. An apparatus according to claim 19 wherein the first couplingcomprises a uni-directional torque transfer mechanism for transferringmechanical energy associated with the motion of the one or more jointsin a first direction to the generator and for decoupling the transfer ofmechanical energy associated with the motion of the one or more jointsin a second direction opposite the first direction from the generator.22. An apparatus according to claim 19 wherein the first couplingcomprises a mechanical rectifier connected such that motion of the oneor more joints in a first direction causes corresponding motion of amechanical rectifier output component in a corresponding first directionand motion of the one or more joints in a second direction opposed tothe first direction causes corresponding motion of the mechanicalrectifier output component in the corresponding first direction.
 23. Anapparatus according to claim 9 wherein the first coupling comprises atransmission for altering torque and speed characteristics of themechanical energy associated with the motion of the one or more jointsprior to transferring this mechanical energy to the generator.
 24. Anapparatus according to claim 9 wherein the first coupling comprises aload leveling device for adjusting temporal fluctuations in themechanical energy associated with the motion of the one or more jointsprior to transferring this mechanical energy to the generator.
 25. Anapparatus according to claim 3 wherein the controller is configured toassess whether motion of the one or more joints is associated withmutualistic conditions or non-mutualistic conditions based at least inpart on a model of repetitive motion of the body of the human or animal.26. An apparatus according to claim 25 wherein at least one of the oneor more sensed characteristics comprises a characteristic associatedwith the repetitive motion of the one or more joints.
 27. An apparatusaccording to claim 3 wherein at least one of the one or more sensedcharacteristics is related to an angular characteristic of the one ormore joints and the controller is configured to process the at least oneof the one or more sensed characteristics to obtain an angular positionof the one or more joints and an angular velocity of the one or morejoints.
 28. An apparatus according to claim 27 wherein the controller isconfigured to assess whether motion of the one or more joints isassociated with mutualistic conditions or non-mutualistic conditionsbased at least in part on detecting one or more zero crossings of theangular velocity.
 29. An apparatus according to claim 27 wherein thecontroller is configured to assess whether motion of the one or morejoints is associated with mutualistic conditions or non-mutualisticconditions based at least in part on comparing the angular position toone or more threshold levels.
 30. An apparatus according to claim 3wherein at least one of the one or more sensed characteristics isrelated to an angular characteristic of the one or more joints and thecontroller is configured to process the at least one of the one or moresensed characteristics to obtain an angular position of the one or morejoints.
 31. An apparatus according to claim 30 wherein the controller isconfigured to assess whether motion of the one or more joints isassociated with mutualistic conditions or non-mutualistic conditionsbased at least in part on comparing the angular position to one or morethreshold levels.
 32. An apparatus according to claim 3 wherein at leastone of the one or more sensed characteristics is related to an angularcharacteristic of the one or more joints and the controller isconfigured to process the at least one of the one or more sensedcharacteristics to obtain an angular velocity of the one or more joints.33. An apparatus according to claim 32 wherein the controller isconfigured to assess whether motion of the one of more joints isassociated with mutualistic conditions or non-mutualistic conditionsbased at least in part on detecting zero crossings of the angularvelocity.
 34. An apparatus according to claim 26 wherein the modelpredicts that the motion of the one or more joints is associated withnon-mutualistic conditions during a particular portion of the repetitivemotion and the controller is configured, for that particular portion ofthe repetitive motion, to refrain from decoupling the at least one of:the mechanical energy associated with the motion of the one or morejoints from the generator and the electrical output of the generatorfrom the load.
 35. An apparatus according to claim 3 wherein a first oneof the one or more sensed characteristics comprises an activity level ofone or more muscles associated with the motion of the one or more jointsand wherein the controller is configured to assess whether motion of theone or more joints is associated with mutualistic conditions ornon-mutualistic conditions based at least in part on comparing theactivity level to one or more threshold levels.
 36. An apparatusaccording to claim 35 wherein a second one of the one or more sensedcharacteristics is related to an angular characteristic of the one ormore joints and the controller is configured to process the second oneof the one or more sensed characteristics to obtain an angular velocityof the one or more joints and the controller is configured to assesswhether motion of the one of more joints is associated with mutualisticconditions or non-mutualistic conditions based at least in part ondetecting a sign of the angular velocity.
 37. An apparatus according toclaim 1 wherein the apparatus is mountable to the body of the human oranimal and the one or more joints comprise one or more joints of thebody of the human or animal.
 38. An apparatus according to claim 1wherein the apparatus is embedded into an interior of the body of thehuman or animal and the one or more joints comprise one or more jointsof the body of the human or animal.
 39. An apparatus for harvestingenergy from motion of one or more human or other animal joints, theapparatus comprising: a generator for converting mechanical energy intocorresponding electrical energy; a first coupling for transferringmechanical energy associated with motion of one or more human or otheranimal joints to the generator; a second coupling for transferringelectrical energy output of the generator to a load; one or more sensorsfor sensing one or more corresponding characteristics associated withthe motion of the one or more joints; and a controller connected toreceive the one or more sensed characteristics and configured to assess,based at least in part on the one or more sensed characteristics,whether motion of the one or more joints is associated with mutualisticconditions or non-mutualistic conditions, and if the controllerdetermines that the motion of the one or more joints is associated withnon-mutualistic conditions, to disengage at least one of: the mechanicalenergy transfer of the first coupling; and the electrical energytransfer of the second coupling.
 40. An apparatus for harvesting energyfrom motion of one or more human or other animal joints, the apparatuscomprising: means for converting mechanical energy associated with themotion of one or more human or other animal joints into electricalenergy; means for assessing whether the motion of the one or more jointsis associated with mutualistic conditions or non-mutualistic conditions;and means for completing a coupling of mechanical energy associated withthe motion of the one or more joints to the converting means andelectrical output of the converting means to a load if the assessingmeans determines that the motion of the one or more joints is associatedwith particular mutualistic conditions; and means for disengaging atleast one of: mechanical energy associated with the motion of the one ormore joints from the converting means; and electrical output of theconverter from the load, if the assessing means determines that themotion of the one or more joints is associated with non-mutualisticconditions.
 41. An apparatus for harvesting energy from motion of one ormore human or animal joints, the apparatus comprising: a generatorcoupled to one or more human or animal joints and to a load forconverting mechanical energy associated with motion of the one or morejoints into corresponding electrical energy delivered to the load; oneor more sensors for sensing one or more corresponding characteristicsassociated with motion of the one or more joints; and a controllerconnected to receive the one or more sensed characteristics andconfigured to assess, based at least in part on the one or more sensedcharacteristics, whether motion of the one or more joints is associatedwith mutualistic conditions or non-mutualistic conditions and, if thecontroller determines that the motion of the one or more joints isassociated with non-mutualistic conditions, to decouple at least one of:the generator from the one or more joints; and the generator from theload.
 42. An apparatus according to claim 12 wherein, if the controllerdetermines that the motion of the one or more joints is associated withthe particular mutualistic conditions, the controller is configured toengage energy harvesting by switching the mechanism to its engagedconfiguration and wherein, if the controller determines that the motionof the one or more joints is associated with non-mutualistic conditions,the controller is configured to disengage energy harvesting by switchingthe mechanism to its disengaged configuration.
 43. An apparatusaccording to claim 23 wherein the transmission comprises a gear train.44. An apparatus according to claim 37 wherein the one or more jointscomprise the knee of the human or animal body.
 45. An apparatusaccording to claim 25 wherein the model of the repetitive motion of thehuman or animal body comprises a model of the repetitive motionassociated with walking.